Preeclampsia is a trophoblast-induced disorder of pregnancy with characteristics of a multisystem disease, resulting from an adverse maternal response to (in part) allogenic placental tissue. Preeclampsia is a heterogeneous disorder. Therefore, generalization of results from different studies is difficult and clear definitions are essential. The exact etiology of preeclampsia is still a matter of debate and many theories have been proposed. It is unlikely that a single factor underlies the development of preeclampsia. This review describes definitions of hypertensive disorders in preeclampsia and summarizes the most important pathophysiologic mechanisms.