This article explains why there is important variation in the degree of concentration of legislative specialization across legislative parties. Greater concentration of legislative specialization leads parties to concentrate their legislative efforts on a smaller set of policy jurisdictions. Through enhancing their concentration of legislative specialization in certain policy areas, parties might more clearly signal their policy concerns and interests to voters. This study argues and shows that party size alters the concentration of legislative specialization. In particular, I find that a U-shaped curve defines the relationship between party size and the degree of concentration of legislative specialization: niche parties and the largest parties choose higher levels of concentration of legislative specialization.
