A very clearly written introduction to cryptography. The presented material is illustrated with many examples and notes, so that the text can be recommended to every novice in the subject. The reader finds information on all useful basic topics and results as well as comments outlining research topics. The book consists of 6 chapters (the English edition does not contain Chapter 6 of the Russian original, entitled “Computer and Cryptography'”), which are written by different authors and which can be read independently of each other to a certain extent. For instance, the last Chapter 6 is based on problems offered at the Russian “Cryptography Olympiads for High School Students” since 1991. Its understanding requires almost no knowledge beyond standard high school mathematics. The previous five chapters of the booklet provide the reader with the most basic notions and techniques used in the contemporary symmetric and asymmetric cryptosystems. All notions like one-way functions, one-way trapdoor functions, key exchange protocols, or zero-knowledge protocols are discussed in a highly lucid way. Attractive themes like coin flipping over the phone, basic algorithmic number theory (including RSA, factorisation and primality), complexity questions for some number-theoretical algorithms or threshold secret sharing schemes are not missing. The book is well-motivated and can be recommended as first reading to everybody interested in cryptography.