The topic of prosocial behavior (e.g. fairness, solidarity, and altruism) has recently shifted back into the center of attention in a variety of disciplines, ranging from economics across sociology and psychology towards biology. It is now a well-accepted fact in all human sciences that human behavior is not always governed by egotism and selfish motives. Unfortunately, this does not explain why human also act blatantly selfish and are blind to the suffering of others. This book is a response to the quandary. It brings together leading researchers in sociology and psychology to explain human egotism and altruism using not only their area of study but also bringing in research from economics and biology. Since this work brings together the research of many different disciplines, a complete account of solidarity and prosocial behavior is presented.