Artificial chemistries are presented. An informal definition is first introduced, followed by a presentation of the various kind of artificial chemistries found in literature. We continue explaining the difference betweena qualitative model and a quantitative one. We then explain how a.c. presents a qualitative model, more than a quantitative one. The common measures used to follow the behaviour of an a.c. experiment are then introduced. Artificial chemistries generate particular algebraic structures: organisations. Organisations are then defined, and some of its basic algebraic properties presented. The general behaviour of an experiment is then presented. The article ends with an example of a particular artificial chemistry.