This book highlights contributions from leaders in the feld of sigma receptor research. Sigma receptors represent a promising, novel target for the treatment of neurodegenerative diseases, retinal degenerations, pain and substance abuse. Information is presented about tracers for molecular imaging these receptors, the newly determined crystal structure of human sigma 1 receptor and information about sigma 2 receptor. New discoveries about the role of sigma 1 receptors in cancer, pain, neuropsychiatric disorders, learning and memory, neuronal networks and depression are described. The compendium offers important insights about the direction unfolding for this exciting feld of research.