The book "Polar cap magnetic activity (PC index) and space weather monitoring" offers a comprehensive analysis of the PC index, which was originally developed as a measure of magnetic activity in the polar regions. This index is considered an indicator of the energy that enters the magnetosphere during the coupling between solar wind and magnetosphere. The authors, Oleg Troshichev and Andrezen, explore various aspects of the PC index, including its derivation methods and its relationships with interplanetary electric fields as well as different types of magnetospheric substorms and magnetic storms. The book also highlights the response of the PC index to seasonal variations in ionospheric conductivity and its ability to predict magnetic disturbances. These features make the PC index a valuable tool for monitoring and forecasting space weather events based on regular magnetic observations in the polar regions.