The objective of this article is to present a theory that analyzes the effects of legislative institutions and party discipline on policy stability. In this paper, I generalize Krehbiel’s (1998) U.S. lawmaking model by reformulating it within the veto player framework. A major finding of this article is that legislative institutions have differential effects on policy stability depending on party discipline, and that party discipline also has differential effects depending on legislative institutions. This article also yields two important results that do not support the conventional wisdom that divided government works better with party indiscipline and unified government does better with party discipline. First, the cause of non-differential lawmaking across government types in the U.S. Congress is not party indiscipline but legislative institutions that provide both of the governing and opposition parties with symmetric veto powers. Second, gridlock not only occurs but also increases under unified government with a disciplined majority under the U.S. legislative rules.