A contract of employment is an agreement between an employer and an employee. The employee is obliged to do work, and the employer is obliged to pay for it. This is enshrined in the Civil Code. This agreement may be written orally, in which the written version is the most predictable and also advisable (to prevent problems and ambiguities and to be demonstrable). An employee is always a physical/natural person, an employer does not have to be, that is often a legal entity (eg, membership, etc.).