SPM is defined as “the planning, monitoring and controlling of project delivery and support processes, with consideration of the environmental, economic and social aspects of the life-cycle of the project’s resources, processes, deliverables and effects, aimed at realising benefits for stakeholders, and performed in a transparent, fair and ethical way that includes proactive stakeholder participation.” [4]. This definition highlights that SPM is about the integration of sustainability into the processes and practices of project management. Several studies identified the ‘impact areas’ where an integration of sustainability would impact the processes or practices of project management. Table 1 summarises these impact areas, as found in the literature on SPM, organised by phase of a project life cycle.

The maturity of integrating sustainability considerations in project management can vary by project type or industry due to specific sustainability challenges, regulatory requirements, available resources, and stakeholder expectations.

For example, as the construction industry dramatically contributes to environmental impacts such as carbon emissions, waste generation, and resource depletion [22,23,24], several industry standards and regulations have been developed aimed at reducing these negative impacts through sustainable design, choice of material, construction techniques and methods, and complying with regulatory requirements. Standards such as BREEAM (Building Research Establishment Environmental Assessment Method) and LEED (Leadership in Energy and Environmental Design) are well established and are driving the integration of sustainability in construction. Although these standards were originally mainly focused on the sustainability quality of new buildings, they have expanded their focus and today encompass the whole life cycle of buildings, from planning to in-use and refurbishment. Therefore, the maturity of sustainability considerations in building projects is expected to be quite high.

Sustainability standards can also be found for event projects. The ISO 20121 standard [25] describes a management system that has been designed to help organisations in the events industry improve the sustainability of their event-related activities, products, and services. The standard aims to describe the building blocks of a management system that will help any event-related organisation reduce its environmental footprint and become more socially responsible while remaining financially successful. ISO 20121 applies to all types and sizes of organisations involved in the events industry, from caterers, lighting and sound engineers, security companies, stage builders and venues to independent event organisers and corporate and public sector event teams. The maturity of sustainability considerations in event projects is, therefore, also expected to be high.

Another industry at the forefront of sustainable development is the energy industry. As this industry is critical to transitioning to renewable energy sources and reducing carbon emissions, organisations are experiencing a lot of societal and regulatory pressure to develop and implement renewable energy projects. This pressure and competitive market forces around renewable energy can also drive the maturity of project sustainability considerations.

The manufacturing industry is a significant consumer of natural resources and can generate large amounts of waste and pollution; therefore, sustainable project management must focus on reducing the environmental impact of manufacturing processes through waste reduction, energy efficiency, and sustainable material sourcing.

Given the functional ability of information technology (IT) and information systems (IS) to improve, change and reinvent business processes, IT/IS is considered to be an important contributor to more sustainable business practices [26]. However, IT/IS is also recognised as having a significant negative impact on the environment, as the IT industry is responsible for 2% of global CO₂ emissions, which is equivalent to the amount generated by the aviation industry [27]. It is for this reason that sustainability should be an important consideration in IT/IS projects. For this reason, sustainability should be an important consideration in IT/IS projects. Despite the environmental impacts of IT/IS, both positive and negative, Watson et al. [28] conclude that the IS community is largely unaware of these impacts. More recently, Asadi et al. [29] concluded that current knowledge about the sustainability impacts of IT/IS is still limited and that there is a need for a “better understanding of the multifaceted nature of green IT and the strategies and approaches that organisations can follow to green their IT” [29]. These indications suggest that the maturity of sustainability considerations in IT/IS projects may not be that high.

The evidence discussed above suggests that the consideration of sustainability may be more prominent in certain types of projects, most likely construction, energy, and events projects, than in other types, such as IT/IS projects. In addition to expectations about the extent to which sustainability is taken into account, it can also be expected that the diversity of projects will influence the materiality of different sustainability aspects. Moreover, particular industries and project types will, therefore, consider certain sustainability aspects more prominently than other industries or projects.

In addition to the type of project or industry, other situational variables may also influence the consideration of project sustainability. For example, the size of the project or the number of organisations or stakeholders involved. Small projects tend to be less complex than larger projects and may have fewer stakeholders. Sustainable project management for small projects may focus on identifying and mitigating potential negative environmental, social, and economic impacts of the project. It may depend highly on the resources available for sustainability initiatives, such as financial, human, and technological resources. Average-sized projects may have a moderate level of complexity; sustainable project management may focus on developing and implementing stakeholder engagement plans, sustainability goals, and sustainability reporting frameworks influenced by project team support. Large projects can typically be highly complex, with multiple stakeholders and sustainability challenges. These include integrating sustainability into project management processes and practices, such as risk and impact assessment and monitoring, while ensuring adequate levels of leadership commitment, stakeholder engagement and resource availability for sustainability initiatives. Therefore, it is expected that the size and number of partners involved in the project will influence the maturity of sustainable project management.

The “maturity” of sustainability considerations in a project can be assessed using the Sustainable Project Management Maturity Model (SPM3) developed by Silvius and Schipper [8]. SPM3 is one of the few sustainability assessment tools developed specifically for projects [30], and its application has been reported in several studies—for example, Esezobor [31], Simionescu and Silvius [32], Clinning and Marnewick [33], and Marnewick [34]. SPM3 provides a descriptive maturity model with which organisations can assess their level of sustainability integration in a given project and develop insights on how to improve this consideration of sustainability in projects.

SPM3 structures the assessment of various sustainability impacts into 22 indicators of different aspects of sustainability, as shown in Table 2. The indicators are organised from the triple bottom-line perspective of economic, social, and environmental indicators.

The SPM3 assessment assesses the consideration of the various aspects of sustainability on a four-level maturity scale: (1) compliant—projects at this stage have little consideration of sustainability and are focused only on meeting requirements; (2) Reactive—projects’ sustainability practices are ad hoc; at this stage, projects are beginning to consider sustainability but have yet to integrate it thoroughly and consistently into project management; (3) Proactive—projects have established sustainability objectives, policies, and procedures and are integrating them into project management; and (4) Purposeful—projects have embedded sustainability into project management practices and are monitoring sustainability performance; sustainability practices are consistent and well documented, and projects are striving to measure and optimise sustainability impacts.

SPM3 covers both the sustainability by the project and the sustainability of the project, as identified by Huemann and Silvius [1] and Sabini et al. [6]. Sustainability by the project refers to the sustainability of the project’s outputs or outcomes. In contrast, the sustainability of the project refers to the sustainability of the project’s planning, management, and implementation processes, as shown in Table 1. The reporting format of SPM3 (Figure 1) shows the assessment of the consideration of the 22 different aspects of sustainability separately for the project process, expressing the sustainability of the project perspective, and for the project product, expressing the sustainability by the project perspective. Both assessments are expressed in the four maturity levels mentioned earlier.

Since SPM3, like most maturity models, is designed as a tool to support the development of the consideration of sustainability, it is suggested that each individual aspect of sustainability be assessed twice: once as an assessment of the “actual” situation in the project (indicated in black in Figure 1) and the second time as an assessment of the “desired” situation in the project (indicated in middle grey in Figure 1).