In a project network, a dependency is a link amongst a project's terminal elements.

There are four kinds of dependencies with respect to ordering terminal elements (in order of decreasing frequency of use):

1. Finish to start (FS)
   • A FS B = B doesn't start before A is finished
   • 
   • (Foundations dug) FS (Concrete poured)
2. Finish to finish (FF)
   • A FF B = B doesn't finish before A is finished
   • 
   • (Entire book written) FF (Last chapter written)
3. Start to finish (SF)
   • A SF B = B doesn't finish before A starts
   • 
   • (New shift started) SF (Previous shift finished)
4. Start to start (SS).
   • A SS B = B doesn't start before A starts
   • 
   • (Project work started) SS (Project management activities started)

There are three kinds of dependencies with respect to the reason for the existence of dependency:

1. Causal (logical)
   • It is impossible to edit a text before it is written
   • It is illogical to pour concrete before you dig the foundations
2. Resource constraints
   • It is logically possible to paint four walls in a room simultaneously but there is only one painter
3. Discretionary
   • I want to paint the living room before painting the dining room, although I could do it the other way round, too

Traditional critical path-derived schedules are based only on causal (logical) dependencies. The critical chain method necessitates taking into account resource constraint-derived dependencies as well.