EU law is widely recognized as the backbone of European integration. As ''the Guardian of the Treaties'', the European Commission is expected to enforce EU law relentlessly and meticulously. Noncompliance by Member States, however, is not always prosecuted by the supranational guardian; instead, supranational enforcement by the Commission is known to be selective and strategic. In this book, Yaning Zhang argues that such forbearance is driven by divergent enforcement rationales. He assumes that the Commission, when enforcing EU law, is a hybrid institution of a political agent and a judicial trustee. The enforcement incentives of the Commission are to advance its legislative and political agenda and to safeguard the stability of the EU legal order, respectively. When these two incentives interact, it leads to four ideal types of toleration of noncompliance with EU Law by the Commission. Guided by the proposed typology, the book traces four cases of enforcement leniency concerning restrictive measures against pharmaceutical parallel trade, opaque defence procurement, degrading practices towards irregular migrants, and discriminatory regulation over car tolls. These cases demonstrate that the Commission''s strategic enforcement is not driven by a singular or merely egocentric logic but by different configurations of divergent enforcement incentives. Naturally, the normative quality of individual types of forbearance is also rather diverse. With its novel typology and in-depth empirical evidence, The European Commission''s Toleration of Noncompliance with EU Law offers a new way of understanding the complex interplay between law and politics in the EU.