The EE Organisational Operation Theory or PSI theory is a theory about the operation of organisations. PSI stands for Performing in Social Interaction. Based on the CIAO Paradigm (Communication, Information, Action and Organisation), a communication-centric view is taken on the cooperation of people in enterprises, as manifested in business processes. The fundamental notion in understanding the operation of organisations is the coordination act. It consists of a performer, an addressee, an intention and a product. The performer and the addressee are actors, i.e. subjects filling an actor role. Actor roles are the units of authority and responsibility. Coordination acts can be performed verbally, non-verbally and tacitly. They are the key elements in (business) conversations, which are the constituting parts of (business) transactions. A transaction is carried out by actors in two roles: the initiator and the executor. The executor brings about the product of the transaction. The process of a transaction is a path, possibly including iterations, through a universal transaction pattern, which consists of one main pattern and six revocation patterns. The latter serve to revert the state in the main pattern to a previous state. Because of the inherent connection between an actor role and the transaction kind of which fillers are the executor, the combination of the two is called transactor role. Transactor roles are the universal building blocks of business processes. Performing a coordination act results in creating the corresponding coordination fact. A fundamental principle in the PSI theory is that actors act autonomously, also if they are guided by business rules. Based on this principle, definitions are developed for the notions of authority, responsibility, accountability and competence.