A contract of employment is an agreement between an employer and employee that establishes the employment relationship. Most contracts do not need to be in writing but it is better if they are. The contract begins when an offer is accepted and work starts. A mutual agreement between parties can modify the contract terms outside of the existing agreement. Non-disclosure agreements are commonly used when companies or individuals evaluate potential business relationships to restrict sharing of confidential information. Partnership and collaboration terms are often used interchangeably in policy to describe coordinated efforts between organizations.