On September 11 2001, thousands of people died in the attacks on the United States. How could this act of terror be justified? A young man kills his sister to protect his family's honour. How could this be right? These are just two of the questions tackled by Neil Levy in this guide to the philosophy of moral relativism - the idea that concepts of rightness and wrongness vary from culture to culture and that there is no such thing as an absolute moral code. Opening with a comprehensive definition to this controversial theory, the book examines all the arguments for and against moral relativism, from its implications for ethics to the role of human biology and the difficulty of separating cultural values from innate behaviour. The author draws on case studies from sources as diverse as the Aztecs and the Australian aboriginals to illustrate debates such as: can we ever have a shared morality?; can concepts of rightness and wrongness ever be absolute?; does moral relativism pose a threat to human rights? Concluding with a proposal for a more modest form of relativism, and outlining all the key reading in this area, this introduction should prove enlightening for students and general readers alike.