## 6 Conclusions  
GPP allows for the creation of competitive environments that reward higher sustainability performance than any required by regulation, facilitated through the use of voluntary standards in public tenders that help to qualify, quantify, and guide sustainability improvements. In this way, voluntary standards serve as a linchpin between missions and concrete projects, and their presence, type, and means of use can be an indicator for tangible progress toward achieving missions. This may be particularly true in the absence of coordinated, outcome-oriented methods for assessing progress, such as widespread, routinized procedures to follow up on actual performance upon project completion. For SUD projects where the municipality is not the landowner, private project developers must only adhere to public policy requirements. If these are perceived as the bare minimum in terms of sustainability performance, additional agreements between parties can lead to the incorporation of higher standards. Whether or not this is occurs depends on many aspects, such as on individuals employed for the project and on whether an area is appointed as a pilot area. Progress toward missions is often requested across all districts of a municipality, for the city as a whole, such as by its alderman for urban planning and sustainability. However, this is difficult because of differences in organizing document sources, leaving it difficult to understand what is happening, with policies leaving room for interpretation that results in high variability between districts. To reduce variation between sustainability ambitions between districts, policies should be similarly approached in all documents. Due to the high influence that individual project members can currently have on project sustainability, standardizing processes are expected to create more clarity for project developers and facilitate interest in voluntarily increasing sustainability performance of non-tender projects particularly. For the cases examined in this paper, and likely for many other municipalities globally, the processes for incorporating sustainability missions--as well as the sustainability missions themselves--are new. The use of voluntary standards in GPP is similarly novel; however, there is a growing awareness and understanding of the mechanism, where its practical implementation can feed into theoretical assessment, and vice versa. Studies on implementation of GPP to support missions can therefore lead to a greater scientific understanding of the interaction between sustainability missions and other themes is necessary to explore the potential trade-offs and unintended consequences of incorporating these missions--including via voluntary standards--into GPP. Providing means by which to improve the use of voluntary standards in tender projects is therefore recommended to increase competition for sustainability within suppliers operating in the construction sector and indirectly influence environmental performance within the SUD MIS. Finally, the conclusions of this paper present opportunities for further research. Due to the high number of projects analyzed and the variance between these projects, it was not possible to go in-depth into the results of either subset of tender projects or non-tender projects. To derive meaningful results, this paper therefore focused on tender vs. non-tender projects, also to better highlight the role of voluntary standards and GPP within SUD projects as a whole and toward municipal missions that affected both project types. Since an in-depth look into the formulation and specification of voluntary standards within tendering documents themselves is valuable in providing greater understanding into the ways in which they are deployed in practice toward sustainability missions, future research should undertake this more focused investigation. An extension of this limitation is the focus on the demand-side rather than any micro-level analysis of the supply-side.