The paper discusses the relationship between intelligence services and national security, or the significance of intelligence services’ impact on the national security of any country. The author starts by stating that this relationship is often simplified, within the following pattern: domestic intelligence services (always) work towards achieving and preserving the national security of their own country, and foreign intelligence services (always) threaten and impair this security. Using the comparative historical method and methods of analysis and synthesis, the author subjects this pattern to criticism, stating, first, that domestic intelligence services (both at national and subnational level), in addition to the expected positive, i.e. constructive action, may also act destructively to national security. On the other hand, he maintains that foreign intelligence services, in addition to predominantly destructive effect on national security of other countries, may also have a positive impact. Offering ample evidence for both of these assertions, the author concludes that the relationship between the intelligence services and national security is much more complex than many people might think, and that it does not do with any simplifying and easily launched patterns.