Maternal obesity is associated with increased morbidity and mortality for both mother and offspring. The mechanisms underlying the increased risk associated with maternal obesity are not well understood. In non-pregnant populations, many of the complications of obesity are thought to be mediated in part by inflammation and its sequelae. Recent studies suggest that a heightened inflammatory response may also be involved in mediating adverse clinical outcomes during pregnancy. This review summarizes our current knowledge about adipose tissue biology, and its role as an endocrine and inflammatory organ. The evidence for inflammation as a key mediator of adverse pregnancy outcome is also presented, focusing on the role of inflammation in adipose tissue, systemic inflammation, the placenta, and vascular endothelium.