Exploring the vocabulary of declassified elements (criminals, street children, beggars, tramps, prostitutes, etc.), the author tells how jargon arose and developed. Numerous jargons taken from special studies and personal observations are cited. The book is intended for everyone who is interested in this specific branch of the Russian language. Why is a policeman called a cop? It turns out that the word "cop" came to us from the Polish language... And when a criminal pricks out on his body "I will not forget my mother," do not rush to be touched: he does not mean the woman who gave him life. Jargonisms need to be studied, says the author of this book. But do not clog the Russian language with them.