The purpose of the graduation thesis is to research and present the role of key performance indicators in mobile networks management. In the first part, the development of mobile technologies and the importance of key performance indicators in mobile networks are presented. Data traffic is persistently growing, therefore, the mobile networks constantly develop. That means that networks are more and more difficult to manage. With the help of the key performance indicators, the operator can successfully monitor the service quality. The key performance indicators are defined in 3GPP specifications, and some are defined by the equipment manufacturer. In order to calculate the key performance indicators, we need the data that can be obtained from three sources, namely measurements in network element, measurements of signalling, and periodic tests. In the third chapter, architectures of 2G, 3G, and 4G networks are presented as well as descriptions of network elements. The central part presents the relevant indicators of performance for all three mobile networks. Each mobile technology has a lot of key performance indicators, therefore, the operator must decide which of them are relevant for him. We have divided the key performance indicators into the following groups: network accessibility, mobility, voice services, packet data services, VoLTE, SMS and network elements operation. For each group, the relevant key performance indicators were chosen, which must be monitored by the operator in order to ensure smooth operation of the services. The last part deals with the approach in mobile network management by using the key performance indicators. A network operations center is presented which monitors measurements and alarms. Further, the difference between the measurements and alarms is explained, and which groups of the key performance indicators are monitored in the network operations center. It is also described who needs the access to the measurements or key performance indicators and why. In the conclusion, it is explained why the key performance indicators are important. Findings for individual services are also stated.