In the past few decades, the spread of the Internet and the emergence of electronic commerce (e-commerce) or online shopping have changed the way consumers think and live in an unprecedented trend [1]. With the exponential growth of mobile devices (mainly smartphones) in the last decade, mobile commerce (m-commerce) has emerged, once again changing consumer behavior patterns and dramatically changing the landscape of traditional e-commerce [2]. It means that consumers can make purchases using their smartphones anytime, anywhere. Technology advancements have given rise to new business models and consumer-friendly services, such as mobile payments and online bookings [3]. Online-to-offline commerce (O2O commerce), which has recently been very popular, is one of those new business models. In O2O commerce, consumers typically make the purchase online and then consume the products or services offline [4,5]. To illustrate, consumers search, book, or pay online using a mobile app. They subsequently use location services to find and walk into the target brick-and-mortar store to consume. Alternatively, they receive products or services at home or at the workplace using instant delivery or door-to-door services.

O2O commerce combines online and offline channels, which means bringing online consumers into “real-world” stores [6] or using the online channel to drive offline sales [7]. For those brick-and-mortar businesses that have been impacted by e-commerce and feel left out, O2O commerce brings them new opportunities [8]. The enormous potential profit drives many local businesses or merchants into the O2O market [9]. Meanwhile, O2O commerce also brings great convenience to consumers. One of the most visible examples is the O2O food delivery services [10], which have been widely discussed, especially during the COVID-19 pandemic [11,12]. In addition, the “stay-at-home order” policy in the pandemic has prompted some traditional brick-and-mortar retailers to offer home delivery services through O2O platforms [13].

O2O commerce is growing and expanding rapidly along with the development of mobile Internet and information technology [14]. In addition, since the outbreak of the COVID-19 pandemic, more and more offline businesses are using O2O platforms to find their customers [13,15]. Although O2O commerce has been very popular and has shown to be a successful business model [8], its sustainability is unknown. The rapid expansion of O2O commerce has raised concerns that this business model may not be sustainable [16]. It is necessary to identify current trends in O2O commerce to inform the development of sustainable strategies and the implementation of sustainable management. However, no review paper has attempted to discuss the research and industry trends in O2O commerce. Therefore, one of the objectives of this paper is to identify these trends by reviewing the current literature.

Due to the intense competition in the market, most O2O players tend to focus on increasing sales rather than on developing a sustainable relationship with consumers to maintain their business [17]. In the past few years, many O2O-related start-ups have failed, and one possible reason is that they did not closely observe consumer behavior [18]. In order to increase their survival chances, O2O businesses must retain existing customers and attract new ones by understanding consumer behavior to ensure the sustainability of their business. Digitization has extended to all stages of consumers’ purchases [3], making consumer behavior more complex than ever, especially in O2O commerce, as it simultaneously involves online and offline channels. It is worth acknowledging that because O2O commerce is a new and emerging business model, limited studies have attempted to understand these complex consumer behaviors. Thus, another objective of this paper is to synthesize previous studies to understand the factors influencing consumers’ O2O behavior.

Similar to other terms of e-commerce such as consumer-to-consumer (C2C) and business-to-consumer (B2C), online-to-offline (O2O) is a type of e-commerce business model. Rampell [6] first proposed the concept of O2O in 2010 and illustrated that the key to O2O is to find consumers online and bring them into offline channels. Tsai et al. [2] argued that O2O commerce provides a seamless purchasing experience between online and offline commerce by any connected device, while Xiao et al. [19] stated that O2O commerce brings offline business activities to online channels which are used to promote offline businesses. Some researchers have distinguished between online-to-offline and offline-to-online commerce [20,21,22]. Although the specific wordings differ, according to Ryu et al. [23], O2O commerce is an integration rather than a competition between online and offline channels, creating new values. In the past, O2O commerce attracted consumers with banner advertisements and digital coupons [7]. Nowadays, O2O commerce plays an essential role in different scenarios of consumers’ lives [12] and covers many types of local businesses, such as catering, ticketing, car-hailing, etc. [23].

Alternatively, O2O commerce can be viewed as an extension or upgrade of traditional e-commerce [19,24,25]. There are several differences between O2O commerce and traditional e-commerce. First, O2O commerce is location-based [2] and focuses on local retail and life service industries [19,26], such as restaurants, hotels, and entertainment. Second, the transactions in O2O commerce typically involve both online and offline channels [27,28]. Third, the features of O2O commerce make it difficult for consumers to return goods as easily as in traditional e-commerce [9,19]. Last, O2O commerce involves more participants, including consumers, offline stores, online platforms, and third-party service providers [29]. O2O commerce extends the scope of traditional e-commerce activities [30].

Business models always seem to change with the evolution of technology [2]. Many new types of O2O commerce are springing up, such as O2O clothing customization [31] and O2O community e-commerce [32]. There are many different scenarios in O2O commerce, but the two most apparent market segments in O2O industry practice, namely, “to-shop” and “to-home” [33,34], are rarely mentioned. The former refers to in-store consumption after paying or booking online. In contrast, the latter refers to receiving products or services at home or at the workplace through instant delivery or door-to-door services.

Consumer behavior involves many things. It reflects the totality of consumers’ decisions in terms of “the acquisition, consumption, and disposition of goods, services, activities, experiences, people, and ideas by (human) decision-making units” [35]. Consumer behavior includes the consumers’ emotional, mental, and behavioral responses that precede, determine, or follow activities such as purchasing, using, and distributing goods and services [36] (p. 8). Although research has shown that consumer behavior is difficult to predict, it has always been an area of interest for scholars and marketers. Back in the 1960s and 1970s, Howard and Sheth [37] and Fishbein and Ajzen [38] proposed traditional models to explain consumer behavior. As e-commerce became popular, some researchers argued that online consumer behavior is different from offline behavior, and that new theories or models are required [39].

A review paper by Hwang and Jeong [40] discussed the factors affecting consumer behavior in e-commerce from the individual, website, and environmental dimensions and reported that many constructs had been used to study online consumer behavior. Technology acceptance and use behavior has been the subject of many classic studies in e-commerce. Haryanti and Subriadi’s [41] literature review showed popular theories and models in e-commerce research, namely TRA [38], TPB [42], TAM [43,44], UTAUT [45], and UTAUT2 [46] (see Table 1）。他们还发现了这些理论和模型之外的变量，其中信任和感知风险是最广泛使用的。此外，DeLone 和 McLean [ 47 ] 开发的信息系统成功模型 (ISSM) 和 Bhattacherjee [ 48 ]提出的期望-确认模型 (ECM)已被用于解释消费者在电子商务中的采用和使用持续行为。许多研究 [ 49 , 50 ]。 表 1显示了这些理论和模型中影响电子商务中消费者行为的外生变量。

然而，在 O2O 商务方面，情况似乎变得更加复杂，因为它包括线上和线下渠道。王等人。[ 30 ]指出，搭便车和陈列室是全渠道市场（即O2O市场）的典型消费者行为。搭便车是指消费者在一个渠道搜索信息并在另一个渠道购买 [ 51 , 52 ]。消费者通常会比较不同的渠道，然后选择附加值更高的渠道购买产品或服务[ 53 ]。陈列室是指消费者在网上选择商品，线下购买[ 54 ]，体现了消费者在保证产品功效的前提下追求交易成本最小化[ 55 ]]。此外，与传统电子商务相比，O2O 商务涉及更多的参与者和技术创新，使得消费者行为更加复杂。例如，O2O 交易包括在线撮合、在线支付、线下消费等活动 [ 29 ]，以及定位系统、近场通信 (NFC) 和快速响应 (QR) 码 [ 22 ] 等技术。

与传统电子商务类似，O2O 商务可以被消费者视为一种创新的信息技术服务，因此技术使用文献对于理解与 O2O 服务相关的消费者行为是相关的[ 56 ]。以前的模型或构造已被用来解释 O2O 商务中的消费者行为，最广泛关注的是 TAM 和服务质量（例如，[ 20 , 57 ]）。然而，由于影响消费者 O2O 行为的因素已经被松散地理论化，讨论一直是零星的和有限的。例如，O2O 外卖中讨论的食物选择动机 [ 58] 可能不适用于其他 O2O 场景。此外，需要更多的证据来证明先前电子商务文献中应用的理论和模型可以解释 O2O 环境下的消费者行为。