Politicians' personal beliefs and backgrounds strongly influence politics and policy. But why do individuals with particular beliefs and backgrounds tend to run for office and become politicians? This paper argues that parties and interest groups strategically shape the candidate pool from which voters choose by mobilizing certain individuals to run for office, much like they strategically shape the electorate by mobilizing like-minded individuals to vote. Supporting this view, I first unearth decades of previously disparate evidence suggesting that candidate mobilization efforts are widespread. I then present results from an experiment embedded in an actual candidate mobilization effort that finds encouragement to run for office can meaningfully increase interest in candidacy. Implications and opportunities for further research are discussed.