The main goal of this bachelor thesis is to prove the significance of assertive behaviour and communication of a manager. In theoretical part of the thesis the term assertiveness is defined, assertive communication is contrasted with other styles of communication and not least the best known assertiveness techniques are characterized and analysed. The practical part presents results of a research which is realized by means of the questionnaires compiled on the basis of theoretical findings. The aim of the research is to find out whether managers consider assertiveness to be an integral part of managerial skills and how important particular assertiveness techniques are.