Our research mainly develops in the field of differential equations; more precisely, in the qualitative theory of ordinary differential equations. In particular, in the study of dynamical systems in the plane. The problems in which we are or we have been interested are: The integrability problem (theory of Darboux, Lie, Painleve), the center-focus problem and computation of Poincaré Liapunov constants, the isochronicity problem, the reversibility problem, nilpotent and degenerated systems, bifurcations, theory of limit cycles (16th problem of Hilbert), Lie symmetries, differential equations in the complex projective plane, etc.