Why do some rules have the status of law while others do not? Is law simply a matter of rules anyway? What is justice? Is there a duty to obey a law even if it is unjust? Should the law concern itself with the activities of consenting adults in private? This fully-updated new edition of Legal Theory asks questions such as these, discusses topical issues such as animal rights, and explains some of the answers which legal theorists have given from Ancient Greece to the present day. Written in a very readable style, this book makes intrinsically difficult material accessible and interesting.