CONTENTS Introduction CHAPTER I. Generalization of the second Lyapunov method § 1. Lyapunov functions that are positive-definite in part of the variables § 2. Equipotential surfaces of the perturbed Lyapunov function § 3. Lemma on the proximity of solutions of the systems (1) and (3) § 4. Investigation of stability by means of a perturbed Lyapunov function defined on an annular domain § 5. Investigation of stability over a finite interval § 6. Investigation of stability in higher approximations § 7. Theorems on instability in the "neutral" case CHAPTER II. Investigation of the stability of resonance problems § 1. Statement of the problem § 2. Investigation of the stability of systems of equations of the form (1.1) having an asymptotically stable averaged system in the single frequency case § 3. Investigation of the stability of systems of equations of the form (1.1) having an asymptotically stable averaged system in the multi-frequency case § 4. Investigation of the stability of a multi-frequency system for a finite time interval CHAPTER III. Investigation of the stability of orbits in the three-body problem § 1. Canonical variables, equations of motion, and integrals of motion in the three-body problem § 2. Resonance curves and the choice of new variables § 3. Construction of a perturbed Lyapunov function and investigation of stability in the three-body problem References