The classification of attractors, from a computational point of view, can be made using as a criterion the simplicity of detection their basin of attraction. Taking into account this classi cation criterion, recently a concept of hidden and self-excited attractors was proposed. An attractor is called a hidden attractor if its basin of attraction does not intersect with small neighborhoods of equilibria, otherwise it is called a self-excited attractor. Self-excited attractors can be localized numerically by a standard computational procedure, in which after a transient process a trajectory, starting from a point of unstable manifold in a neighborhood of unstable equilibrium, is attracted to the state of oscillation and traces it. For localization of hidden attractors it is necessary to develop special procedures, since there are no similar transient processes leading to such attractors. This survey is dedicated to ecient methods for the study of hidden attractors.