We study the performance of two-sided matching clearinghouses in the laboratory. Our experimental design mimics the Gale-Shapley (1962) mechanism, utilized to match hospitals and interns, schools and pupils, etc., with an array of preference profiles. Several insights come out of our analysis. First, only 48% of the observed match outcomes are fully stable. Furthermore, among those markets ending at a stable outcome, a large majority culminates in the best stable matching for the receiving-side. Second, contrary to the theory, participants on the receiving-side of the algorithm rarely truncate their true preferences. In fact, it is the proposers who do not make offers in order of their preference, frequently skipping potential partners. Third, market characteristics affect behavior and outcomes: both the cardinal representation and the span of the core influence whether outcomes are stable or close to stable, as well as the number of turns it takes markets to converge to the final outcome.