Border activities are aimed at ensuring national security in the border space. They can be treated as a system of preventive measures (border prevention and containment), security and control measures (border service and search), and protective and combat measures (special and combat actions, operational actions). Functions (stages of the activity cycle) are assigned to each type of boundary measure. Border measures can be implemented via operations carried out throughout the country, one or several federal subjects according to a single plan for achieving a specific goal. The problems of border activities are investigated in the science of border activities--the system of knowledge to ensure border security, build state border organizations, prepare and conduct border activities, and provide comprehensive support of border activities. The substantial aspects of the science of border activities are studied. The principles of border activities are systematized as follows: activity, the secrecy and surprise of actions, flexibility, complex use of forces and means, the continuity of actions in place and time, the concentration of main efforts on the key directions and tasks, interaction, international cooperation, the main link, the balance of security and freedom, deterrence, reliance on the local population, the primacy of preventive measures, a combination of traditional and new technologies, and a comprehensive assessment of border security.