ABSTRACT Within the clear definition of a quick clay as being a soil which has a sensitivity greater than 30 and a remoulded strength less than 0.5 kPa, a general model for quick clay development is presented, based on the influences of various material properties and natural processes on the sensitivity and remoulded strength. The influences are separated according to depositional requirements and post-depositional factors and according to whether the influence is to increase the undisturbed strength or to decrease the remoulded strength. Depositional factors are the requirements for a flocculated structure and the dominance of low activity minerals. Post-depositional factors are cementation and slow load increase, which increase the undisturbed strength, and little consolidation, leaching and dispersants, which decrease the remoulded strength. The application of the model to marine, brackish water and freshwater sediments is discussed.