Breach of contract is when one party to a lease, written or oral contract fails to fulfill their duties without a valid legal excuse. As a concrete example, take the landlord-tenant relationship. When a tenant signs a year-long lease, he or she usually agrees to live in the residence, abide by the rules and pay the rent by the due date. If a tenant fails to pay the rent according to the terms of the lease, then he or she is in breach of contract. The landlord can then take the tenant to court and recover damages. A breach of contract is also common in real estate sales because many potential buyers sign a contract as part of the sale process. If the buyer finds another property and decides to purchase it instead, he or she may be found in breach of contract and have to purchase the original property or pay some type of penalty.