Algebraic set theory was introduced by Joyal and Moerdijk in their book from 1995 and is an approach to the semantics of set theory based on categorical logic. One of its strengths is that it gives a uniform approach to set theories of different kinds (classical and constructive, predicative and impredicative). In addition, it allows one to capture different kinds of semantics (forcing, sheaves, boolean-valued models, realizability) in one common framework. In this talk, I will give an introduction to the subject, concentrating on main ideas rather than technical details.