After more than a century of intensive research, pre-eclampsia and eclampsia remain an enigmatic set of conditions. Aberration of the interaction between placental and maternal tissue is probably the primary cause, but the exact nature of the differences from normal pregnancy remain elusive. In this review attempts to understand the sequence of physiological changes have concentrated on vascular endothelium and oxidative stress issues. There are genetic components to susceptibility, but the relative contributions of maternal and fetal genotypes are still unclear. Whole-genome mapping could ultimately define the causative genes.