An employment contract or contract of employment is a kind of contract used in labour law to attribute rights and responsibilities between parties to a bargain. The contract is between an "employee" and an "employer". It has arisen out of the old master-servant law, used before the 20th century. But generally, the contract of employment denotes a relationship of economic dependence and social subordination. In the words of the controversial labour lawyer Sir Otto Kahn-Freund,
"the relation between an employer and an isolated employee or worker is typically a relation between a bearer of power and one who is not a bearer of power. In its inception it is an act of submission, in its operation it is a condition of subordination, however much the submission and the subordination may be concealed by the indispensable figment of the legal mind known as the 'contract of employment'. The main object of labour law has been, and... will always be a countervailing force to counteract the inequality of bargaining power which is inherent and must be inherent in the employment relationship."
A contract of employment usually defined to mean the same as a "contract of service". A contract of service has historically been distinguished from a contract for the supply of services, the expression altered to imply the dividing line between a person who is "employed" and someone who is "self-employed". The purpose of the dividing line is to attribute rights to some kinds of people who work for others. This could be the right to a minimum wage, holiday pay, sick leave, fair dismissal, a written statement of the contract, the right to organise in a union, and so on. The assumption is that genuinely self-employed people should be able to look after their own affairs, and therefore work they do for others should not carry with it an obligation to look after these rights.
In Roman law the equivalent dichotomy was that between locatio conductio operarum (employment contract) and locatio conductio operis (contract for services).
The terminology is complicated by the use of many other sorts of contracts involving one person doing work for another. Instead of being considered an "employee", the individual could be considered a "worker" (which could mean less employment legislation protection) or as having an "employment relationship" (which could mean protection somewhere in between) or a "professional" or a "dependent entrepreneur", and so on. Different countries will take more or less sophisticated, or complicated approaches to the question.