## 6 Conclusions  
This paper examines the impact of winning a public contract on innovation with environmental benefits in EU enterprises, using CIS 2014 survey data and the PSM model. The findings suggest that the companies who have won public contracts are 5.7% more likely to bring in innovations with environmental benefits than their counterparts. The \"dual-impetus\" framework to interpret PP's positive influence on eco-innovation is creatively constructed in this paper. One rationale is \"regulatory effect\" by Environmental Innovation Theory, or government as regulator by Stakeholder Theory, or \"coercive pressure\" to firms by Neo-institutional Theory. This rationale is commonly possessed by innovation policies. The other rationale is \"demand pull\" by Environmental Innovation Theory, or government as customer by Stakeholder Theory, or \"normative pressure\" to firms by Neo-institutional Theory. This rationale is distinct and unique for PP, granting it additional potential to achieve policy goals compared to other environmental regulations. The customer is core stakeholder for private companies; public customer is not different in this respect. Government expenditure reaches almost 20% of GDP in EU, and the public contracts are usually of large volume and value. Furthermore, the governments can lead in their role and open the early market. Theoretically, public procurement takes the advantage from extra demand effect over other innovation policy and shall be investigated in depth. In this sense, the potential of PP to promote innovative or eco-innovative activities has been underestimated. As the results display, the effect of PP on innovations with different environmental benefits varies. Compared with eco-innovation that occurred within the enterprises, it is easier for PP to stimulate firms' eco-innovations during the consumption and use of goods or services by the end user. What is more, environmental innovations in recycling both within the companies and by end users are evaluated to be promoted by public contracts. In detail, PP is tested to be effective on innovations of five environmental benefits: recycled waste, water, and materials for own use or sale (firms with a public contract are 3.3-4.5% more likely to achieve that than firms without a public contract); reduced energy use and CO\({}_{2}\) footprint by end users (3.1-4.2%); reduced air, water, noise, and soil pollution by end users (5.4-5.7%); facilitated recycle of the product after use (2.6-3.4%); and extended life length of the product (2.9-3.4%). The underlying reason for the positive effect on recycling and on the environmental activities of end users may be that the corresponding green criteria could be employed more readily in the technical specifications, selection criteria, award criteria, and contract performance clauses in a procurement project. When examining the award criteria documents in the EU, the most frequently occurring green words relate to air pollution, waste water, recycle, reuse, repair, and the warranty of the targets [69]. Except for the PPI, green criteria embraced along the procedures of GPP is the main mechanism of the effect and the key to its success [70]. The inclusion of green criteria, their measurability and evaluability could be the priorities to maintain and enhance the policy effect. This study also analyzes the subgroups by firm size, cooperation, nation, and industrial sector. The results demonstrate that PP impels small and large enterprises to make eco-innovation decisions, of the magnitude of 5.0-6.3% and 7.5-10.6%, respectively, while it does not obviously work on medium-sized ones. Small firms have more adaptable structures and preferential treatment in PP policy. Large companies possess larger competitive abilities and R&D capabilities to win the public tenders. The results from [PERSON] and [PERSON] [34] were not exactly the same, where the effect was statistically significant for SMEs while not for large companies.