This book is the result of research done in the last two years by the "Group of Nonlinear Analysis" (GANol) of the Faculty of Exact and Natural Sciences and Surveying of the National University of the Northeast (UNNE). Here we present some qualitative results refereed to the generalized Liénard's equation and systems. The main tool is the Lyapunov's Second Method and the results obtained englobes common and non-usual conditions.