 What reasons do promisors have to keep promises? How do these promissory come about and how do they function? How strong are they, and what, if any, reasons may override them? These are just some of the most common questions in this area, and the literature on them is quite large, too large to adequately survey here, so I will just note some important foci. Of particular interest are the answers to these questions provided by Joseph Raz (1975, 1982, 1986, 2012).