Research on evaluation has mainly focused on the use of evaluation and has given little attention to the origins of evaluation demand. In this article, I consider the question of why parliamentarians demand evaluations with parliamentary requests. Building on the literature of delegation, I use a principal-agent framework to explain the origins of evaluation demand. In doing so, I argue that the parliamentarians mainly demand evaluations in order to hold the government accountable. The quantitative analysis shows that Swiss parliamentarians demand more evaluations if they have the impression that the administration does not implement the policies within their meaning. This finding suggests that parliamentarians demand evaluations in order to fulfill their oversight function towards the government. This conclusion could be relevant in order to understand the role of evaluations within the parliamentary arena.