Anyone subject to the Market Rules is a rule participant. Since different rules relate to different types of participants, a number of Rule Participant classes are defined. A rule participant can belong to more than one class, except where this is explicitly restricted.

The WEM Rules place the obligation to register as a rule participant on owners, operators, and controllers of facilities. If more than one person is involved, and if those people reach an agreement as to which of them will become a rule participant for the purposes of the WEM Rules, AEMO can exempt the others from being rule participants.

A rule participant that participates in any aspect of the reserve capacity mechanism, bilateral trade, the STEM, or the dispatch/balancing process, is referred to as a market participant. A party that is both a market generator and a market customer is a single market participant.

With the exception of AEMO and System Management, parties wanting to become a rule participant must apply to AEMO. In applying for rule participant status, a party must accept the obligation to comply with the relevant Market Rules.