Chapter 3 studies VSS under EU competition rules. While in the debate on competition law and sustainability it is often argued in favour of a larger space for private sustainability initiatives, the chapter studies the possibility of using competition rules to tackle the implications of VSS especially on prices and market access. The chapter focuses on the Commission Guidance on Horizontal Agreements, under which standard-setting in line with procedural requirements is seen as pro-competitive. By employing empirical research on the market impact of VSS and economic literature, the chapter argues that VSS can result in restrictions to competition and it questions whether a hands-off competition treatment of VSS is warranted. This finding is assessed against the current approach for balancing pro- and anti-competitive effects of agreements as applied by the Commission. The chapter then suggests a possible approach under Art. 101 TFEU for a thorough scrutiny of economic and non-economic effects of VSS. Chapter 3 also studies VSS under rules for dominant undertakings and considers whether recognition of VSS at the national level would exclude the application of competition rules.