Reciprocity is the exchange of goods or services without formal currency or contract. It works on social obligation, not legal enforcement. You give something now because you expect something later, or because you owe something from before. The exchange may be immediate or delayed by years. It may be balanced, with equal value given and received, or generalized, where no one keeps score.

Marshall Sahlins distinguished three forms. Generalized reciprocity occurs among close kin, where sharing is expected and repayment is loose. Balanced reciprocity involves direct exchange between people who are not intimates, with an expectation of equivalent return within a reasonable time. Negative reciprocity is an attempt to get something for nothing, through haggling, theft, or exploitation. The same people may engage in all three, depending on the relationship.

Examples in daily life

• Sharing meat after a hunt.
• Helping a neighbor build a house.
• Exchanging gifts at holidays.
• Bartering at a market.

Reciprocity binds people together. It creates trust, obligation, and the expectation of future interaction. Markets can function without it. Communities cannot.