Mercury (Hg) is a global pollutant that knows no environmental boundaries. Even the most stringent control of anthropogenic Hg sources will not eliminate exposure given its ubiquitous presence. Exposure to Hg occurs primarily via the food chain due to MeHgs accumulation in fish. Latest US statistics indicate that 46 States have fish consumption advisories. In addition, Hg is a common pollutant in hazardous waste sites, with an estimated 3-4 million children living within one mile of at least one of the 1,300+ active hazardous waste sites in the US. The effects on intellectual function in children prenatally exposed to MeHg via maternal fish consumption have been the subject of two on-going major, prospective, longitudinal studies in the Seychelles and the Faroe Islands. It is important to recognize that the risk for MeHg exposure is not limited only to islanders with high fish consumption. This book will provide state-of-the-art information to the graduate student training in toxicology, risk assessors, researchers and medical providers at large. It is aimed to bring the reader up to date on contemporary issues associated with exposure to methylmercury, from its effects on stem cells and neurons to population studies.