This chapter describes key developments in financing congressional campaigns and campaign costs since the 1970s. These developments can plausibly influence challenger quality in congressional elections. The chapter examines the impact of campaign costs and campaign spending on candidate emergence in elections for Congress. While campaign spending is not exactly a measure of campaign costs, campaign finance data can serve as a useful indicator of cost available at the district level. Campaigns spend money because they feel they need to do so in order to win. Rising advertising costs—especially broadcast advertising on television—are likely to be at least partly responsible for rendering political campaigns more expensive over time. Estimating campaign costs, and evaluating developments in campaign costs over several decades, is a tall task. One plausible explanation for incumbents' campaign funding advantage is the role played by political action committees. These groups have become key players in financing congressional campaigns since the 1970s, and their resources have been directed toward incumbents.