Transaction costs are the various expenses a company incurs when it considers outsourcing an activity to a third party. These costs include, among other things: 1) expenses related to researching and initially negotiating a contract with a business partner (including any intermediary commissions), 2) the costs of monitoring the proper execution of the contract, 3) potential losses due to an initial contract that is ill-suited to reality, 4) costs related to a possible renegotiation of the contract, and 5) opportunity costs resulting from tying up capital to guarantee compliance with the terms of the contract (through hedges, guarantees, etc.).

Oliver Williamson is recognized for having deepened and enriched the field of transaction economics, while as early as 1937, Ronald Coase was the first to consider that companies could constitute an alternative to market-based cost coordination, thus laying the foundations of transaction cost theory. In this context, Carole Donada and Gwenaëlle Nogatchewsky explain that transaction cost theory (TCT) highlights the fact that the characteristics of transactions (their level of uncertainty, their frequency, the degree of specific assets or investments required) as well as the context in which they occur (number of actors involved, degree of opportunism, level of rationality) lead to costs that impact performance. To minimize these costs, it is crucial to choose the most appropriate forms of organization and contracts: the market (conventional contract), the hybrid form (neoclassical contract), or hierarchy (integration). Within the transactional approach, agency theory and contract theory provide two conceptual frameworks.