Yes. When you start a project it is visible only to you, then you can click on the 'Team' button in your publishing dashboard as depicted below  and add your team members via their email addresses as either a "keeper"  or a "writer".  

Keepers have almost all the same permissions as you, the book creator, so that you can delegate administrative tasks to others if you like and "writers" can only edit content but cannot see or manage all of the other project details.