Among his main results are the development of the theory of hidden oscillations and the concept of self-excited and hidden attractors, the discovery of a hidden Chua attractor in Chua circuits, revealing of coexisting hidden attractors in electomechanical models with Sommerfeld effect, a solution of the Gardner problem on the lock-in range for phase-locked loops, counterexamples with self-excited and hidden attractors to the classical describing function method,