The article deals with the issue of the relationship between the legislative and the executive powers under the presidential and semi-presidential systems of government. The starting point is the following general remark. While the presidential system is characterized by a consistent or complete separation of powers, the semi-presidential system — being typically mixed with a parliamentary system — treats the principle of division of powers in a less restrictive way, allowing — just like a parliamentary system — various kinds of exceptions to the rigid separation of powers. Consequently, in both of these systems the relationships between the legislature and the executive are arranged somewhat differently. Under the presidential system these relationships are kept to a minimum, and the collision between the legislature and the executive occurs episodically and mainly in the context of competition between them, whereas under the semi-presidential system various kinds of contacts between the legislative and the executive are acceptable and more frequent. While the presidential system is generated by competition between powers, the semi-presidential (and parliamentary) systems is based on the idea of cooperation of powers. Thus, under the general idea of cooperation the legislature and the executive much more likely enter into various kinds of arrangements (eg. a legislative initiative of the government, the procedure for holding the government politically responsible). It should, however, be noted that both described systems of government in its pure form are rare. Clear presidential system is in fact the political system of the United States, while the proper semi-presidential system exists in the French Fifth Republic. All other systems, conventionally classifi ed as one or the other category, are in fact more or less departure from them and rather form a wide range of neo-presidential or para-presidential regimes.