Quantum Theory from a Nonlinear Perspective : Riccati Equations in Fundamental Physics This book provides a unique survey displaying the power of Riccati equations to describe reversible and irreversible processes in physics and in particular quantum physics. Quantum mechanics is supposedly linear invariant under time reversal conserving energy and in contrast to classical theories essentially based on the use of complex quantities. However on a macroscopic level processes apparently obey nonlinear irreversible evolution equations and dissipate energy. The Riccati equation a nonlinear equation that can be linearized has the potential to link these two worlds when applied to complex quantities. The nonlinearity can provide information about the phase amplitude correlations of the complex quantities that cannot be obtained from the linearized form. As revealed in this wide ranging treatment Riccati equations can also be found in many diverse fields of physics from Bose Einstein condensates to cosmology. The book will appeal to graduate students and theoretical physicists interested in a consistent mathematical description of physical laws. Introduction Time Dependent Schrödinger Equation and Gaussian Wave Packets Time Independent Schrödinger Equation and Riccati Equations Dissipative Systems with Irreversible Dynamics Irreversible Dynamics and Dissipative Energetics of Gaussian Wave Packet Solutions Dissipative Version of Time Independent Nonlinear Quantum Mechanics Nonlinear Riccati Equations in Other Fields of Physics Summary Conclusions and Outlook.