This paper adapts a simple model from the optimal contracting literature to explain the relationship between political parties and non-incumbent candidates. The model predicts that legislators with a higher opportunity cost of government service will receive better committee assignments. Using data that spans 12 Congresses (97th to 108th), I find that when the opportunity cost of Senate service is measured by previous occupation, freshmen senators with a high opportunity cost for serving (those who were lawyers) were given good committee assignments, while freshmen senators with a low opportunity cost for serving (professors, and those with relatives already in politics) were given worse committee assignments. Copyright Springer Science+Business Media, Inc. 2006