This chapter examines the political dynamics of legislative scrutiny, with an emphasis on how parliamentary policy influence works. A central function of legislatures is legislating. In the case of the UK Parliament, the treatment of legislation is one of the most time-consuming activities, with both Houses spending the great majority of that time scrutinizing government bills. The chapter first introduces the reader to common assumptions, including the idea that government dominates the process, with Parliament acting as little more than a ‘rubber stamp’, before questioning these various assumptions. It shows that non-government amendments may ‘fail’ but can nonetheless be influential, that government amendments do not necessarily imply government dominance, that the two Chambers often operate in cooperation rather than competition, and that parliamentary influence occurs throughout the policy process. Furthermore, the chapter suggests that the legislative process is less separate from other processes than it might appear.