This analytical study evaluated the development of the security environment of the Czech Republic in 2021. The study is based primarily on materials prepared by the Centre for Security and Military Strategic Studies, as well as on analytical materials prepared in countries which share the same or similar security environment and security interests. The study presents the results of a comparative analysis of available open sources and contains an evaluation of selected state and trans-national actors. For the purpose of the study, a sectoral analysis based on the principles of the Copenhagen School was used, describing the political, social, environmental, military, technological and economic sectors. The study analyses the period of the past year 2021 and tries to capture the main events and trends in specific sectors with impact on the security environment and to identify the implications for defence policy and the armed forces. The results of the sectoral analysis are shown by the figure at the end of the study. Relevant threats identified in 2021 are aligned with the corresponding sectors, i.e., according to the nature of the protected value or the interest of the Czech Republic, which are endangered (e.g., the stability of the Euro-Atlantic area or the environment). At the same time, the threats are placed in homocentric circles reflecting the levels of their instrumentality: local - regional - global. Some of the challenges are manifested across multiple sectors and levels.