A comprehensive SQE overview of several legal doctrines that can affect the validity and enforceability of a contract, primarily focusing on circumstances where consent may be compromised or the contract's purpose is unlawful. Misrepresentation is explained as a false statement of fact that induces a contract, categorized as fraudulent, negligent, or innocent, with different remedies available for each. The sources then detail Mistake, where a fundamental error—such as common, cross-purpose, or unilateral—can render an agreement void because there was no genuine meeting of the minds. Furthermore, the texts explore Duress and Undue Influence, describing how coercion through physical, psychological, or economic threats, or the improper leveraging of a position of trust, makes a contract voidable. Finally, Illegality is covered, clarifying that contracts are unenforceable if their formation or purpose violates statutory law or common law principles, such as public policy or committing a crime.