This book has been published in order to solve nonlinear vibration problems in engineering and basic sciences. Definitely, solving nonlinear differential equations governing physical phenomena can be considered as the root of most researches and studies in the applied sciences. In addition, the obtained results have been utilized in order to design, implement, and apply in industry. It is necessary to mention that the behavior of most phenomena is engineering and basic sciences is revealed as non-linearity, so to comprehend the relationships among the components of each phenomenon, having sufficient mathematical knowledge is very essential. Up to here, a big step has been taken in understanding the relations among the elements of physical phenomena. In the next steps, it is important to solve nonlinear differential equations. Since every differential equation consist of a series of independent and dependent variables and has some parameters with respect to the physical propertiesof the system, it is better to solve differential equations analytically in terms of their parameters.