This book is a continuation of the previous issue (129) of the Quantum Library. In two books all published in the journal "Quantum" articles of one of the most constant and favorite authors - Moisey Isaacovich Kaganov, a theoretical physicist, a specialist in the field of quantum theory of a solid body, one of the brightest representatives of the Landau school . are collected together. Articles in collections are arranged in chronological order. The first article was published in the journal "Quantum" No12 in 1970, the last article (published only in this issue of the Library "Quantum") entered the editorial office in October 2013 The book is addressed primarily to those young people who see themselves as a physicist in the future. But, of course, it will be interesting to the widest range of readers ..