Preeclampsia is one of the main causes of maternal and perinatal mortality in the world; however, the pathophysiologic pathways haven't been clearly elucidated. It is thought to result from a breakdown of maternal tolerance to paternal antigens in placenta that start an immune response against the trophoblast inducing a defective placentation and a hipoxic/isquemic environment which in turn triggers a systemic inflamatory response. This review gives an overview of the mechanims involved in maternal tolerance, how these are disrupted in preeclampsia, and how they contribute to the inflamatory response.