Performance of contracts (Sections 37-67) means execution of contractual obligations. Kinds: Actual performance (complete fulfillment) and Substantial performance (nearly complete with minor deviations). Performance requirements: (1) Proper time—on specified date or within reasonable time; (2) Proper mode—as contract stipulates; (3) Proper place—where contract specifies; (4) Proper person—party owing obligation or authorized agent. Tender of performance: Unconditional offer to perform; sufficient if other party rejects. Doctrine of substantial performance: Minor deviations don't discharge performer's liability for full payment if contract substantially performed. Joint obligations: All parties must perform unless contract indicates alternative. Divisible contracts: Performance divides into installments; breach of one doesn't excuse entire contract. Case law: Planche v. Colburn establishes substantial performance principle. Concurrent conditions: Parties' obligations must be performed simultaneously unless otherwise agreed. For accountants, audit performance requires substantial completion within scope; minor matters don't excuse client payment. Exam tip: Distinguish actual from substantial performance; identify performance conditions; assess whether performer substantially performed.