CONTENTS Introduction Definitions, notation, and results from the theory of quasigroups Chapter I. Identities in systems of quasigroups § 1. Definitions and examples § 2. General identities § 3. Conjugate identities § 4. Some remarks on hyperidentities § 5. Generalized identities Chapter II. Functional equations on quasigroups. Systems of quasigroups with generalized associative, medial and transitive laws § 1. General associative law § 2. General medial law § 3. General transitive equation § 4. General distributive law § 5. General Stein identity. Orthogonal quasigroups Chapter III. Systems of quasigroups with generalized distributive law § 1. The connection of D-systems with commutative Moufang loops § 2. Maximal D-systems § 3. Commutative D-systems § 4. Properties of the transition permutations § 5. A criterion for generalized distributivity § 6. Homogeneity of the operations in a D-system Chapter IV. Systems of quasigroups with generalized Stein identity § 1. Definitions § 2. Auxiliary results § 3. Idempotence of the operations in D-systems § 4. Interdependence of n and s § 5. Connection between S-systems and D-systems §6. Complete S-systems References