Rapid and unprecedented urbanization affecting the globe in recent decades is widely recognized as undermining human health, social stability, and economic prosperity [1]. Moreover, uncontrolled densification has led to a loss of urban green spaces and biodiversity [2]. In response to significant socio-ecological challenges, cities worldwide are implementing programs oriented to healthier design, sustainable planning, and greenification [3]. An incremental application of nature in the city through Nature-Based Solutions (NBSs) is turning the concrete jungle into an urban forest, reconnecting the anthropogenic habitat to the biosphere [4]. Among NBSs, Green Infrastructures gained strategic resonance expanding landscape planning into a more robust urban design thinking [5] and acting as “projective ecologies” of green spaces [6]. All such actions are efficient at reducing the environmental impact and achieving ecosystem service goals, but they neglect various social implications, notably the effects of nature on the health and well-being of millions worldwide, who suffered from its absence or enforced distance during the COVID-19 pandemic [7]. This circumstance unveiled not only the vulnerable interdependencies between humans and nature but also the reciprocity between planet resource consumption and threats posed by cities, including deforestation, biodiversity loss, and climate change [8].

Against the relentless migration trend from the countryside to the cities, research indicates that rural living is preferable to an urban lifestyle due to the better environmental quality that assures mental and physical health [9]. Due to modern habits and a rising technology addiction, we spend 90% of our time indoors. Consequently, recent studies unanimously characterize us as an “indoor generation” [10]. Conversely, more and more citizens pay to be immersed in nature, associating it with a restorative praxis for personal well-being [11]. This explains the increasing global attention to Biophilia, which relies on the interaction between humans and nature to enhance urban livability, face climate change, and bolster urban sustainability and resilience [12]. Since the late 1960s, Biophilia has grown in popularity as a love for life and an innate man’s need to affiliate with all living forms and systems [13]. The concept of Biophilia advances the idea that contact with nature plays a fundamental role in human physical and mental well-being [14]. Firstly pioneered as a genetic-oriented process [15], it was further elaborated in scientific theory—known as Biophilic Hypothesis (BET)—built upon the multidisciplinary evidence [14]. Later, Biophilic Design (BD) was introduced as a novel design language aimed at transposing the BET principles into the built environment ^[16][17][18][16,17,18]. Conceived as complementary support to green architecture, BD offers an emotional way to enjoy the space, maximizing nature’s contribution to making our lives healthier, happier, and more productive [19]. BD was very well received by the scientific community owing to an abundance of studies substantiating the impacts of Biophilia on societal, environmental, and economic systems [20]. In slightly more than a decade, BET was also extended to the cityscape, where the need for daily human–nature contact is not optional but essential to ensure a higher quality of life and preserve biodiversity [21]. The application of Biophilia within the urban context is the legacy of a long-lasting intellectual movement deeply rooted in theories and practices intended to integrate nature and design. Over time, this movement has evolved, associating Biophilia with contemporary concepts, such as Green Urbanism [22], sustainability [12], and smart cities [23].

From its initial applications dating back centuries to the newer global movements, Biophilia continues to be considered an emerging research field, and there remain limitations in broader and intersectoral progress [24]. Among the noteworthy issues, scientific objectivity, measurability, and the upscaling process demand further insights. While the concept of Biophilia has gained recognition and support, its scientific foundation is still subjected to ongoing debate, due to the complexity inherent in basic assumptions, such as the human–nature interactions. Since Biophilia involves the emotional sphere, its inherently subjective nature raises scientific inquiries. As hybrid disciplines, design, architecture, and planning are the result of both technological quantities and artistic qualities, but not all spatial qualities are readily quantifiable or standardized [25]. Additionally, recent studies confirmed the complexity of addressing the multidimensional effects of green space, necessitating the integration of diverse research disciplines: the high heterogeneity of study designs, exposure assessments, and outcomes underscore the call for greater rigor, precision, and robustness [26]. Regarding practical application, the beneficial effects of Biophilic Design (BD) have been extensively documented, primarily due to their small-scale and immediate outcomes. Furthermore, BD is substantiated by applied sciences, which illustrate how mathematical models, specifically fractals underlying Biophilia, have significant practical implications for enhancing the built environment and the well-being of its occupants [27]. Yet, although the beneficial effects of Biophilic Design (BD) are well documented thanks to the small-scale and immediate outcomes, the long-term potential of Biophilic Urbanism (BU) offers less evidence, limiting its utilization and investment. Meanwhile, BU is taking place in an increasing number of metropolises, where nature plays a key role in maintaining ecological continuity and safeguarding the local identity within bioregional systems [26].

Through 38 definitions (Table 1), researchers trace its evolution from the initial hypothesis to grounded theory and practical applications. ^[42][127]. After exploring biophilic effects and the related benefits of urban living, we propose Biophilia Upscaling to emphasize the need to extend Biophilia beyond current limits, moving from concept to implementation (applying), from building to city scale (quantitative upscaling), to make its benefits more diversified and impactful for everyone, everywhere (qualitative upscaling). Through these three actions, Biophilia Upscaling exactly matches the three-metric approach guiding this SLR. The existing literature indicates numerous application metrics supporting a robust Biophilia Upscaling through research by design. From BD to BU, researchers present an overview of design criteria or guidelines laid out chronologically and across scales by leading BET scholars, including the following integrations.

3.1. Biophilic Design

3.3.1. Biophilic Design

Based on the literature cornerstones, researchers have identified the evolution of the BD theoretical framework in four major steps (Table 26). While providing different tools, they aim at achieving the primary goals of BD: creating good habitats for people, nature, and living organisms within modern cities; providing settings, activities, and processes that encourage interspecies interaction to mutually enhance living conditions; addressing the deficiencies of contemporary design, which alienated us from nature; and highlighting the benefits of applying Biophilia to the built environment ^[16][19][43][16,19,47]. However, achieving high-performance BD requires consistent adherence to specific biophilic features, as emphasized by Kellert [17]. He first recognized the need to define BD through two dimensions, six elements, and 72 attributes [16]. This framework has been conceived as a valuable toolkit for designers, aiding in their understanding and implementation of Biophilia. As the second benchmark, Browning et al. ^[44][61] suggested a simplified approach grounded in three categories of space–nature interrelation (nature in the space, natural analogs, and nature of the space), with 14 categories and patterns aimed at prioritizing users’ well-being. They were clearly inspired by Kellert’s guidance [16], as outlined in Table 26, where colorful check marks match the common principles of the two frameworks. Later, Kellert together with Calabrese [19] simplified the original theory in the awareness that BD establishes dynamic living spaces able to adapt to different users and their changing needs over time. To this end, they delivered a novel scheme focused on human perception, thus underlining the role of individuals as the essential perceiving subjects in interacting with nature through three potential experiences: direct, indirect, and space and place. Merging the first two frameworks by Kellert [16] and Browning ^[44][61], Kellert and Calabrese [19] reduced the initial 72 BD indicators to 24 experiences and attributes; namely, they turn out to be a selection from the first panel, as indicated by the bold terms in Table 26. As for the fourth framework, Kellert [17] proposed a more complete paradigm for successful BD applications. Conceived as a theoretical-practical guide, it comprises 40 practices related to both the meaningful rationale of BD (values and principles) and the best practices (experiences, elements, application places, and building typologies) to build indoor and outdoor settings or landscapes [17]. Afterward, supplementary metrics were released to facilitate BD applications. Despite referring to the basic approach, they focus on specific aspects or serve as checking indicators of BD quality. Further progress in BD was suggested by McGee et al. ^[45][91] in the form of the Biophilic Interior Design Matrix, comprising six elements and 54 attributes inspired by Kellert’s scheme. Designed specifically for indoor applications, it serves as a resource for interior designers who approach Biophilia in a “do-it-yourself” mode. Lee and Park ^[46][122] proposed a 15-factor hybrid framework for residential environments that merges physical and digital design techniques so as to reach a larger audience, expanding the range of biophilic experiences on three building scales (residential unit, building, and complex scale). Indoor settings constitute the main location where they tested Biophilia in Virtual Reality. Mollazadeh and Zhu ^[47][106] systematized a series of key elements helping to design virtual biophilic settings for BD indoor implementation. While referring to Browning’s three categories of human–nature experience, their factors were tested to simulate only direct contact with nature (nature in the space) within digital environments. Xue et al. [20] developed a 42-item qualitative framework that blends BD features with standards from green building rating systems, such as LEED and BREEAM. This framework is intended to guide the design process toward creating healthier solutions. Lastly, Vileniske et al. ^[48][121] carried out an initial classification of biophilic buildings that reveals the strong correlation between architecture and biophilic properties in terms of human–nature interaction. Table 37). Lastly, Beatley complemented the BU framework with updated concepts of biophilic cities (Table 2), even showcasing best practices, case studies, and successful initiatives all around the world [21]. His argument underscored the necessity for a new mindset and conduct at the individual, social, and political levels. Thus, he provided a list of 12 Ways to Experience Nature in the City, inside or outside, encompassing psychological, cultural, and social experiences. He also advocated for the role of digital technology as an innovative vehicle to empower biophilic benefits via devices and domotics, offering multisensory experiences of nature: the core of Biophilia ^[36][39]. As shown in bold types (Table 37), such a systemic approach incorporates several key elements already featured in his previous BU theories ^[21][35][21,38]. Through this thematic handbook, he sought to overcome the existing constraints of Biophilia Upscaling, especially in addressing urban planning toward a biophilic agenda ^[36][39]. Following him, Newman played a significant role in advancing this complex process. He laid the foundation for the transformation of Green Urbanism into BU, using Singapore as a paradigmatic example of shifting from a traditional “garden or green city” to a biophilic “city in a garden” ^[22][50][22,59]. To supplement their findings, Beatley and Newman [12] jointly made the latest advancement in Biophilia Upscaling: they extended BU to a bioregional scale to emphasize its contribution to making cities more resilient, even enhancing both social and natural capital ^[51][77]. Continuing in the same vein, subsequent research has produced additional metrics for the effective application of BU, addressing practical challenges related to scalability, environmental concerns, and socioeconomic priorities. Cabanek et al. ^[52][103] proposed an integrated Biophilic Streets Design Framework aimed at integrating BU into the urban fabric, beginning at the street level as the gateway to a biophilic city. On a larger scale, the application of BU was examined through its ecosystem capabilities, identifying biophilic services for the mutual benefit of citizens and the natural environment ^[53][78]. Lee and Kim ^[54][112] developed an advanced framework that categorizes BU elements as climate adaptation and mitigation strategies across three dimensions (macro, meso, and micro) and spatial scales (region and city; neighborhood and street; and building). It also included different biophilic methods (natural, technical, and functional) to make a city climate-proof. By examining the relationship between biophilic city indicators and smart city indicators, Tarek and Ouf [23] proposed a comprehensive framework aimed at achieving urban resilience. Reeve et al. ^[55][64] indexed biophilic benefits as functional features, highlighting the valuable contribution of BU in renewing city planning by seamlessly integrating urban greenery and development across scales. In conclusion, it is worth noting the geographical analysis of BU implementation carried out by Carter and Henríquez ^[56][111]. Leveraging Beatley’s indicators within the category “institutions and biophilic governance”, they systematically mapped BU initiatives globally, thus identifying the most successful endeavors in economically advanced countries where governments actively promoted them. The term “Biophilia” comes from the Greek words “bio” (βίος, “life, alive”) and “philia” (φιλία, “love, amity, attachment”); thus, it means “love for life”. Biophilia finds its roots as far back as the 4th century BC, when Aristotle introduced the notion of “philia” as an interspecies relationship, extending its connotation to reciprocity that underpins social, political, and moral values ^[39][42]. However, the term itself was coined by socio-psychologist Fromm in 1964 to highlight the human tendency to preserve every living being, in contrast to notions of “biophobia” (inherited fear of nature and animals) or “necrophilia” (fascination for death) [13]. Even then, he linked this passionate love of life to individual and societal fulfillment across species ^[28][31]. The concept of Biophilia was popularized by Crafoord Prize-winning biologist Wilson in the homonymous book as an innate emotional affiliation of humans to nature and other species or lifelike processes ^[29][32]. Drawing on Evolutionary Biology, he assumed that it is rooted in our genetic attitude to live in direct contact with nature [15]. This inborn attraction to natural settings and alive organisms, with their beauty and complexity, affects our skills and emotions: as a biological vector, it guides human evolution; additionally, it evokes a sense of pleasure or awe, akin to the sublime ^[30][33]. The man–nature interrelation has historically driven humanity in search of the right place to live, even considering both safety and aesthetics ^[31][34]. Joined by social ecologist Kellert, Wilson gathered anecdotal and evidence-based research on biophilic effects from diverse scientific areas to turn his intuition into a ground theory, known as the Biophilia Hypothesis (BET) [14]. They argued that our primitive dependence on nature was retained over time and adapted to artificial habitats, forging unedited connections with them to ensure survival and foster identity ^[32][35]. In an effort to establish a novel research field, they substantiated the mutual advantages of Biophilia for people and the environment [14]. Fifteen years later, Kellert took BET to the next step of development. He translated it into real-world scenarios by coining the term Biophilic Design (BD) to best describe our evolving relationship with the natural world [16]. BD represents a groundbreaking approach to architectural thinking: it aims to provide a fulfilling human–nature experience even indoors by merging Engineering and Landscape Design to bridge the gaps in contemporary building practices ^{[17][18][19][20]}[17,18,19,20]. Beyond green and sustainable architecture, BD is an evidence-based process that uses nature to convert a building into a living organism interacting with the occupants, thereby enhancing their livability and environmental performances ^{[18][19][33][34]}[18,19,36,37]. Next, urban planner Beatley introduced Biophilic Urbanism (BU) to shift in scale and extend the BET to cities, metropolises, and bioregions. His works offer several concepts within the realm of BU. He first associated BU with a creative mix of urban design and commitment to protecting outdoor life across multiple scales, applying a “room to region” approach ^[35][38]. Subsequently, he defined Biophilic Cities as a place where living beings, natural shapes, and systems are perfectly incorporated into buildings and cityscapes, thus prioritizing the need for daily contact with nature in urban design and planning [21]. Finally, he added 16 definitions of Biophilic Cities to emphasize their health-enhancing potential, ecological benefits to experience and safeguard urban biodiversity, and the social role of nature in favoring people-to-people exchanges ^[36][39]. BU carries the global imperative to redefine urbanity ^[37][40]. With this goal in mind, Beatley established the Biophilic Cities Network, a platform involving individuals, organizations, and cities worldwide to include Biophilia in urban policies and practices ^[38][41]. Today, Biophilia is also expressed in forms of activism: Söderlund shed light on biophilic social movements, whose supports strive to change urban planning by sharing actions and desires to create healthier and more pleasing cities [24]. Krčmářová draws a connection between present-day expressions of Biophilia and its very origin: BET issued by Wilson and his successors appears to have been influenced by analogous bottom-up initiatives, notably the American environmental movements that emerged in the 19th and 20th centuries to promote a harmonious relationship between man and the natural environment ^[40][43]. Amidst a multitude of notions and applications, there is a lack of definitions of Biophilia that emphasize its benefits. Hence, the researchers define Biophilia as a “beneficial experience of interacting with nature—in all its forms—through senses and emotions, whose positive effects are mutually increasing in the built environment when designed according to Biophilic Design and Biophilic Urbanism.” This benefit-oriented notion spotlights both the purpose of this paper and its analytical approach. Biophilic Design (BD) and Biophilic Urbanism (BU) offer tangible and daily biophilic experiences within the built environment, across scales. Intensifying natural capital, they amplify its beneficial effects for both individuals and the community. This is why we introduced the term “upscaling”, associating it with Biophilia. The simplest definition of upscaling refers to expanding or increasing the scale, scope, or impact of a particular phenomenon ^[41][126]. A more detailed and ambitious notion implies delivering higher quantity and quality to a larger target over a wider geographical area, more quickly, more equitably, and more lasting