How can we find true or reasonable moral principles to live our everyday lives by? Torbjorn Tannsjo presents 7 radically different moral theories - utilitarianism, egoism, deontological ethics, the ethics of rights, virtue ethics, feminist ethics, environmental or ecological ethics - each of which attempts to provide the ultimate answer to the question of what we ought to do and why. He carefully describes each theory, showing how it works in practice using the 'trolley problem' thought experiments, critically assessing it and putting it into its historical perspective. This third edition contains a new section on population ethics in the chapter on utilitarianism, discusses the impact of recent findings in social psychology on virtue ethics and includes new, clearer applications of the trolley problem.