An activity is a specific item or phase with scheduled dates within a project's schedule. Activities can be organized in a hierarchical structure (sometimes called "work breakdown structure" in the literature), so that a parent activity can have sub-activities up to 5 levels deep. Activities can be assigned to one or more resources with allocated hours.

Project activities are listed in a project's Schedule tab, either in a Timeline view that shows the activity structure, or in a Resource Usage view that groups activity assignments by team member (and other resources). Activities assigned to a project team member are listed by date and alphabetic order on the team member's My activities page.

Activities are specially designed for the planning phase of a project. Consequently only the Project Manager can create, delete, assign or modify activities.

Activities are also used to organize project milestones and to-dos.