One of the ways the Nordic TSOs maintain the security of supply is through frequency control, as the frequency is directly related to good power quality and the stability of the system. The frequency is affected by different operational scenarios, such as power imbalances between production and consumption and level of system kinetic energy (inertia). For frequency control, the TSOs utilize different reserve products. These reserve products are described in this report as well as how the reserves are dimensioned and procured. In addition, the report provides an overview on operational aspects related to frequency control, such as different system states and performance and stability of reserves, and planned changes to frequency control in the Nordic power system.