Abstract: Legal knowledge is a core aspect in compliance. For law to shape behaviour, people whose conduct the law tries to influence should know the law. This chapter reviews the body of existing empirical research about legal knowledge. It assesses the extent to which laypersons and professionals know and understand legal rules across various domains including employment, family affairs, criminal justice, education and health care. This body of work shows that ignorance and misunderstanding of the law are common across these domains. There is variation and for some laws, amongst some people and in some jurisdictions, there is more or less legal knowledge. Also, the review shows that there is evidence that people tend to equate their own norms with the rules of the law. The chapter concludes by discussing what these findings mean for compliance and the way our laws try to steer human and organisational conduct. Here it questions compliance approaches that view it as a linear process from rule to behaviour.