## 2 Research Background  
In 2005, the Dutch national government accepted a motion in the House of Representatives to use their annual spending power to stimulate the market for sustainable goods and services, and to act as a role model. As a result, a policy on environmentally friendly procurement for the national, local and provincial government was developed and implemented. Since then, sustainable public procurement has grown into a multidimensional policy in the Netherlands, encompassing policies on (1) Green Public Procurement (GPP), (2) Bio-based Public Procurement (BPP), (3) International Social Criteria (ISC), (4) Social Return On Investment (SROI), as well as (5) Innovation-oriented Public Procurement (IPP) and (6) Circular Economy (CIE) [6].  
First, the policy on Green Public Procurement (GPP) is aimed at preventing or minimising the negative impact of production and consumption on the natural environment. The GPP policy encompasses a wide range of environmental criteria for groups of products that public organisations frequently procure (e.g., office equipment, uniforms, road works, catering), which must be applied when procuring from these categories [18]. In addition to these compulsory environmental criteria, the policy lists some wishes that the government wishes public procurers to consider in their procurement projects, but that are not compulsory [18].  
Second, the policy on bio-based public procurement (BPP) prescribes the inclusion of natural and renewable materials in the procurement of goods, services, and works. By increasing the demand for bio-based products through their own purchases, the government wants to ensure that more bio-based products are produced and that new bio-based products can be developed and can drive the development of a bio-based economy [19].  
Third, the policy on International Social Criteria (ISC) aims to contribute to the elimination of unfair trade throughout the international supply chain, and to eliminate, for example, child labour, inhumane working conditions, and starvation wages [20].  
Fourth, the policy on Social Return On Investment (SROI) encompasses an approach that aims to increase the employment opportunities for people at a distance from the labour market (e.g., due to long-term unemployment, a partial incapacity to work, or a disability) by encouraging or obliging contractors to include opportunities for people at a distance from the labour market in the execution of the contract [21].  
Fifth, with the policy on Innovation-oriented Public Procurement (IPP), the Dutch national government wants to stimulate the market to come up with innovative and unique solutions to better perform via their procurement or to directly procure innovative solutions [22].  
Sixth, with the policy on Circular Economy (CIE), the Dutch government aims to make suppliers responsible for closing the lifecycle loop and to ensure that materials are not wasted at the end of their lifecycle, thereby contributing to the transition to a circular economy. In a circular economy, there is no linear system with waste at the end of the lifecycle, but rather materials are reused without losing value [23].  
Each of these sustainable public procurement policies has their own initiators, designers, policy briefs, and implementation. For example, the GPP policy is a compulsory nation-wide policy and is implemented in phases in a wide range of public organisations, including municipalities, water boards and provinces, unlike the SROI policy, which is not compulsory for all organisations. In general, all policies aim to make public procurement more sustainable and to use procurement to reach desired outcomes in society; together, they fall under the umbrella concept of SPP.