This paper studies various equivalent characterizations of left semisimple rings from the standpoint of reverse mathematics. We first show that \ is equivalent to the statement that any left module over a left semisimple ring is semisimple over \. We then study characterizations of left semisimple rings in terms of projective modules as well as injective modules, and obtain the following results: \ is equivalent to the statement that any left module over a left semisimple ring is projective over \; (...) \ is equivalent to the statement that any left module over a left semisimple ring is injective over \; \ proves the statement that if every cyclic left R-module is projective, then R is a left semisimple ring; \ proves the statement that if every cyclic left R-module is injective, then R is a left semisimple ring. (shrink)