Predecessors and successors in project management describe activities that depend upon one another to proceed. These dependencies among activities will determine the order in which the project plan proceeds. Predecessors in project management are activities that must begin or end before a successor task can proceed.

Dependencies in project management can occur in four different ways and can have varying relationships depending on the task or project phase:

Finish to Start: Task B cannot begin until task A has been completed

Start to Start: Task B cannot begin until task A begins

Finish to Finish: Task B cannot be completed until task A is completed

Start to Finish: Task B cannot be completed until task A begins

Finish to Start task dependencies, for example, describe a sequence of activities where one task must be completed before another begins. Another type of dependency is a Finish to Finish task dependency, where one task must be completed before another can also be completed.