In order to produce products and services, companies are using various tangible assets such as production equipment and facilities. The goal of the maintenance function is to maintain these assets so they operate safely, efficiently and economically. This function includes technical, administrative and management activities, carried out in order to keep company’s assets in a state, or restore these to a state, in which they can perform the required functions. The activities should be planned and carried out in a way that allows for obtaining the required technical condition, availability, meets the safety requirements for humans and the environment, ensures quality of delivered products and services, and secures the anticipated service life of individual devices. Both effectiveness and efficiency of the maintenance function are very important to each company trying to operate with profit. As follows from the recent research, the performance of maintenance functions in most of the studied companies around the world is in general unsatisfactory, and the underlying reasons of the subnormal behavior are not sufficiently identified, understood and described.   The result of research presented in this thesis is an improvement support system based on an explanatory model of the maintenance function. This model shows the mechanisms interconnecting the motivations, intents and rationale behind the involved actors, entities and maintenance activities, and in this way gains understanding of how, and in what way the total performance of the maintenance function is affected, thereby supporting improvement decisions. As maintenance cost is a sharply increasing part of the operational costs, it is an evident target for operational and managerial improvement. This research area is strongly encouraged by industry, and is becoming a topic of increasing interest in the academia. / <p>QC 20151117</p>