The thesis gives a survey of power transformer monitoring. The main reasons for the development and application of transformer monitoring systems (TMSs) are given, an overview of monitored parameters and parts of transformer is given as well, and monitoring benefits described. Hardware and software structure of the transformer monitoring system KONÈAR TMS is described. This system enables monitoring most of the given transformer parameters and parts. Further, techniques and principal drawings of measurements in the monitoring system are described, and an overview of sensors and systems for measurements is given. Values of calculated parameters are estimated using implemented algorithms that are described, as well as implemented tools, used for getting additional information on the basis of measured and calculated parameters. This information can be used for managing power plants or a power system, or for maintenance purposes. Three different solutions for remote access to the monitoring system are described. These solutions enable exchange of information during local or remote access to the system. Two solutions are standard, while the third is the proprietary protocol of transformer monitoring system KONÈAR TMS. Communication modules for data exchange with other systems in a power plant, witch are implemented in the monitoring system in accordance with standards IEC 60870-5-101, IEC 60870-5-104 and Modbus, are described. Monitoring system networking on different levels is described. Purpose of these networks is distribution of monitoring information to all users who need this information, to use equipment and tools of monitoring system, as well as communication infrastructure more efficiently.