S.Chmutov, S.Duzhin and S.Lando. Vassiliev knot Invariants I. Introduction. The present paper can be considered both as an introduction to Vassiliev's theory of knot invariants and as an introduction to the subsequent papers [CDL2], [CDL3]. Our chief goal was to explain how the initial topological problem of studying the Vassiliev invariants is reduced to a purely combinatorial one.