Defining the dependencies between tasks helps you determine which tasks start when, as well as when the project might finish (Biafore, 2010, p. 70).
Whenever there is a dependency between tasks there will always be a predecessor and a successor.
There are two types of tasks in dependency relationships: the predecessor and the successor. Successor tasks are dependent on predecessor tasks. (Daley, 2011, p. 46)
Task dependency types set the type of relationship between a successor task and its predecessor(s).
For example Building the wall has a finish-to-start dependency with laying the foundation. The foundation must be finished before building the wall can start.
The Four Task Dependency Types in Project ManagementThere are four task dependency types in Project Management. The diagram below illustrates each task dependency type.
Finish to Start
This is the most common dependency type, and is the default type set when you link tasks in Microsoft Project. A Finish-to-Start dependency means a task can't start until its predecessors have finished. In other words Task B can't start until Task A has finished.
Start to Start
A task can't start until its predecessors have started. For example, Task B can't start until Task A has started.
Finish to Finish
A task can't finish until its predecessors have finished. For example Task B can't finish until Task A has finished.
Start to Finish
A task can't finish until its predecessor tasks have started. For example Task B can't finish until Task has started.
Task Dependencies - references and further readingS. Daley. (2011) Microsoft Project 2010 in Depth. Pearson Education, Inc. p.48.
B. Biafore, (2010) Microsoft Project 2010: The Missing Manual (Missing Manuals). p. 70.