This paper studies the relationship between party discipline and discretionary spending with theory and data. We propose a theoretical model in which a politician faces a conflict between her constituents' interests and the party line. Party loyalty is electorally costly for the politician and is therefore rewarded by the party leader with greater amounts of discretionary spending allocated to the politician's constituency. This effect is greater the more intense the conflict between the voters' and the party's interests. Using data on party discipline in the U.S. House of Representatives and federal payments to congressional districts between 1986 and 2010, we provide evidence that increases in legislators' party discipline raise the amounts of discretionary spending their districts receive. The rewards for discipline are larger the greater the gap between the constituents' and party's preferences (i.e., in conservative-leaning districts represented by Democrats or liberal-leaning districts represented by Republicans).