Kidney exchange platforms serve patients who need a kidney transplant and who have a willing, but incompatible, donor. These platforms match patients and donors to produce transplants. This paper documents operational details of the three largest platforms in the United States. It then uses the framework developed in Agarwal et al. (2017) to examine how practical details influence platform productivity. The results show that reducing frictions in accepting proposed matches, frequent matching, and encouraging altruistic donors are important ways in which a platform can increase its productivity.