This chapter examines the question whether a mere agreement of the parties is sufficient to justify the existence of an enforceable contract. Or should evidence be required to show that the promisor was ‘in earnest’, ‘seriously intended’ to enter into an enforceable obligation, or was induced to make his promise only in view of a ‘consideration’, i.e. some sort of counterperformance by the promisee in which the promisor had an interest? The chapter first discusses cases in which a ‘gift’ is promised by one party and then moves to other ‘gratuitous transactions’, focusing on contracts of guarantee, contracts for the use of property, contracts for the management of affairs, offers to contract, and modifications of contract. It also analyses the intention to enter a legal obligation as requirement for a contract to be valid.