Alongside its immediate implications for pregnancy complications, increasing evidence implicates maternal obesity as a major determinant of health in the offspring during childhood and later adult life. Observational studies provide evidence for effects of maternal obesity on the offspring’s risks of obesity, coronary heart disease, stroke, type 2 diabetes and asthma. Maternal obesity may also lead to poorer cognitive performance in the offspring and an increased risk of neurodevelopmental disorders including cerebral palsy. Preliminary evidence suggests potential implications for immune and infectious disease related outcomes. Insights from experimental studies support causal effects of maternal obesity on offspring outcomes, mediated at least in part through changes in epigenetic processes including alternations in DNA methylation, and perhaps through alterations in the gut microbiome. Although the offspring of obese women who lose weight prior to pregnancy have a reduced risk of obesity, to date few controlled intervention studies have reversed maternal obesity and examined the consequences for the offspring. The long term effects of maternal obesity may have profound public health implications and indicate the urgency of studies on causality, underlying mechanisms and effective interventions to reverse the epidemic of obesity in women of child-bearing age and to mitigate its consequences for the offspring.