Arm is splitting up

When I move the Arm IK my arm is splitting up:

This is the file:

Thanks in advance! :slight_smile:

Your mesh has lots of duplicate vertices. In edit mode, select all, W>Remove Doubles. After that, your arm’s weight painting is way off, you’ll have to fix that by hand in weight paint mode. The upper arm bone has a lot of influence on the forearm, and vice verse.

While you’re at it, your pole target roll angle on the arm’s IK constraint is way off. Considering where your elbow target is, it should be something like 60 degrees.