Dr. Saltzman was Derek and Addison's marriage counselor.
When Derek decided to try to repair his relationship with Addison, they decided to go to counseling together. Derek said he needed Addison to move to Seattle, while Addison needed Derek to stop talking to Meredith, which he said he couldn't do because he works with her. They argued until the end of their session.
In their next session, Addison said she'd decided to move to Seattle and Derek said Meredith wouldn't be an issue anymore.
He is a couples counselor in Seattle.