“Josh, Ben and Kasey have played an important role in our success over recent years and all three have secured winner’s medals with the club,” Somerset director of cricket Adam Hurry told the club’s website, external.
“All three players were offered contract extensions, however, they have taken the decision to seek enhanced playing opportunities elsewhere and we must respect that decision.”
Davey, 34, moved to Somerset from Middlesex for the 2014 season and has made 159 appearances for the club across all formats, scoring 1,906 runs and taking 317 wickets.
Green, 27, has taken 99 wickets and scored 770 runs for Somerset in T20 cricket.
Aldridge, 24, signed his first contract with Somerset aged 17 and has made 32 first-class appearances.