Terms weren't announced for either deal Saturday.
Selden, 22, averaged 5.1 points, 1.1 rebounds and 16.9 minutes in a combined 14 games for the Grizzlies and New Orleans Pelicans this past season. Selden, who is 6-foot-5, appeared in all six of the Grizzlies' playoff games and averaged 3.8 points, 1.5 rebounds and 17.7 minutes.
Selden also averaged 18.5 points and 4.8 rebounds in 35 games this past season for the NBA G League's Iowa Energy, a team now known as the Iowa Wolves.
Simmons, 19, averaged 8.7 points, 1.6 rebounds and 2 assists in 37 games as a freshman at Arizona this past season.