Atheism is increasing, but as a phenomenon continues to be at the fringe of current research. Atheist groups and ideologies represent a wide range of attitudes, behaviour and ways of acting towards religion. The lack of a clear definition of what being atheist (or an unbeliever) means today invites us to study the issue in greater depth. This volume represents a first attempt at understanding and scrutinizing atheism, offering both a global perspective as well as specific case studies.