The state dependency diagram (SDD) is presented as an improved model for entity life history states. Entity life histories (ELHs) are used in methods like SSADM*and LSDM**as a means of establishing the stages each entity occurrence goes through in its life, such as creation, deletion etc. However, ELHs are limited to describing states within one entity, whereas the state dependency diagram shows interdepencies between the states of different entities. Once drawn, the state dependency diagram becomes a model whihc can be used for subsequent analysis.