This introduction to the current understanding of cell migration and invasion indicates how these cellular processes are essential in a variety of physiological events, as well as in the pathophysiology of clinical diseases such as cancer, cardiovascular disease and preeclampsia. The various molecular mechanisms the cells use to migrate and invade are described, and assays currently used to investigate these two processes are shown. Finally, clinical examples where there is dysregulation of cell migration and invasion are presented, namely in the development of cancer, cardiovascular disease and preeclampsia.