Equitable intervention into contract law defies easy summary. Apart from equitable remedies to enforce contracts, such as specific performance and injunctions, or to rescind voidable contracts, equitable doctrines perform a number of distinct roles in the formation, modification and enforcement of contracts. Equity recognises more extensive grounds than the common law to set aside agreements based on defective consent. So, while contracts can be rescinded at common law for duress or fraudulent misrepresentation, in equity they can be avoided on the additional grounds of undue influence, unconscionability, non-fraudulent misrepresentation, mistake and under the rule in Yerkey v Jones (1939) 63 CLR 649. Equity can also occasionally modify or prevent contract enforcement even though the bargaining process was not defective. Terms constituting penalties (as opposed to liquidated damages clauses), forfeiture clauses and contractual restrictions on a mortgagor’s equity of redemption belong to this category and can be set aside.

This chapter addresses equitable interests in property. Despite the implementation of the Torrens system of title by registration for land across all the jurisdictions of Australia, equitable interests remain significant. This chapter considers the characterisation of different equitable interests in property, and the key rules used to resolve priority disputes. Finally, this chapter canvasses some areas where equitable rules, or the philosophy underpinning them, have been incorporated into statutory schemes, with protection against unconscionable conduct particularly prominent.

Enforceable promises occur when the promisor can no longer revise her promise because a promise is intended to, and has, changed the promisee's decisions.