This book was conceived at the 2005 methodology workshop in Boulder, Colorado. Its purpose was to provide background reading and a working text for students and researchers being introduced to the principles and practice of linkage and association analysis in the context of twin and family studies of complex traits, including behavioral and psychological traits. It is edited by four of the most interesting and dynamic young researchers in the field, and authored by them and a roster of 25 additional world class experts in statistical, behavioral, and psychiatric genetics.