Switch between sessions in tmux?

Is PREFIX s but the real command is choose-tree. Then you can use it to bind to other key for example to 'S'

bind S choose-tree

http://man.openbsd.org/OpenBSD-current/man1/tmux.1#choose-tree

Use tmux switch -t [target-session] if want to switch instant

You're looking for C-b ( and C-b ). You can find this and many more wonderful tips on the tmux cheatsheet.

CTRL-b s

found it! Alex's answer is awesome as well. Note CTRL-b is my prefix, your prefix could be something else.