Screen is tmux's spiritual predecessor, but it's still used by many today. Screen is not as extensible as tmux, and in fact Vim doesn't play that nicely with Screen out of the box. However, if you're used to Screen and don't want to change your existing workflow, there are a few tweaks you can make to your setup to make the two get along a little nicer.

The Esc key doesn't register correctly in Vim when running through Screen. You might want to add the following to your ~/.screenrc file to fix the Esc key behavior:

# Wait no more than 5 milliseconds when detecting an input
# sequence, fixes Esc behavior in Vim.
maptimeout 5

Screen also sets the $TERM variable to screen, which Vim does not recognize. Update .screenrc to include the following:

# Set $TERM to a value Vim recognizes.
term screen-256color

There are more minor inconveniences when using Vim and Screen together, such as the Home and End keys not registering, for example. Vim Wikia has a great in-depth entry on getting Vim and Screen to play along nicely at http://vim.wikia.com/wiki/GNU_Screen_integration.