This article uses survey respondents’ own reasons for participating or not participating in surveys, as well as experiments carried out over many years, to propose a benefit-cost theory of survey participation. The argument is that people choose to act, in surveys as in life, when, in their subjective calculus, the benefits of doing so outweigh the costs. The process of reaching a decision may be carefully reasoned or it may proceed almost instantaneously, with the aid of heuristics. But regardless of the process, the outcome depends on a judgment that the benefits of acting outweigh the costs of doing so – even if, objectively speaking, the actors are badly informed and their decision leads to an undesirable outcome. The article reviews research on confidentiality assurances and risk perceptions with reference to a benefit-cost theory of behavior, and concludes by suggesting research to test the theory’s predictions and by drawing testable implications for survey practice.