Thesis deals with the institute of the necessary defence in the Czech Republic, Germany and the USA. It examines the conception of the institute in selected countries, both from the perspective of theoretical background as well as particular legislation accompanied by relevant judicial decisions. Special attention is also paid to legal regulation of weapons in relation to this institute. Comparative chapter as the main focus of this thesis compares different elements of conception of the necessary defence in each country, highlights their strengths and weaknesses, and finally outlines de lege ferenda deliberation which might inspire Czech legislators.