It is well known that the debut largely determines the character, and sometimes the outcome of the further game. A new approach to the study of the debut theory - its development not so much in breadth (to search for new original options) as in depth (to detail seemingly long studied along and across systems) and a new information chess field, which arose as a result of the advent of computer knowledge in our life, required a different reflection of the current state of the debut. In the encyclopedia "Modern Chess Debut" offered to your attention, an attempt has been made to provide a complete picture of the state of this most important stage of the chess game in the 90s