COMMUTATORS OF $C^R$-DIFFEOMORPHISMS ACTING ALONG LEAVES Tomasz Rybicki Key words: Group of diffeomorphisms, identity component, commutator, perfectness of groups, foliation. 1991 Math. Subject Classification: Primary 58D05, Secondary 22E65. Abstract: We study whether a $C^r$-diffeomorphism which is isotopic to the identity and preserves leaves of a foliation can be written as a product of commutators. The result and techniques depend on the class $C^r$, where $0\leq r\leq \infty$.