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
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A dropdown menu appears
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Select Assign contacts to projects
You arrive on the Bulk Assign page (this page may take a while to load when there are many contacts)
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There is a column for each project and a row for each contact.
Use the tick boxes dropdown list to add/remove contacts to/from projects (to add a contact to a project, select Enrolled from the dropdown list)
Press Save
The assignments are done and you arrive back on the Contacts page