The Assign Contacts to Projects page lets you assign multiple contacts to multiple projects at once

Watch the walkthrough

Steps

Go to the Contacts page
Select the More Options button
Select Assign contacts to projects
You arrive on the Bulk Assign page
There is a column for each project and a row for each contact. Use the tick boxes to add/remove contacts to/from projects
Press Save
The assignments are done and you arrive back on the Contacts page