Poole’s Casebook on Contract Law provides a comprehensive selection of case law that addresses all aspects of the subject encountered on undergraduate courses. A contract may be deemed illegal or void on grounds of public policy. This chapter examines the illegality of contracts under English law, contracts prohibited by statute (express prohibition), and contracts that are illegal in their performance. It considers contracts that are void on grounds of public policy, focusing on contracts in restraint of trade, covenants between employer and employee, exclusive dealing agreements, exclusive service agreements, and severance of the objectionable parts of covenants. The chapter also discusses the recovery of money or property transferred under an illegal contract, along with the UK Law Commission’s proposed reform of the law governing illegal contracts and the Supreme Court decision of Patel v Mirza over controversy concerning the nature of illegality, the basis for intervention in illegal contracts, and the ability to recover under an illegal contract.