This book presents some of the most recent results in the field of nonlinear analysis. Dedicated to Themistocles M. Rassias on the occasion of his 60th birthday, this volume contains 44 articles on various developments in the field, pertaining to subjects such as the stability of functional equations, variational systems, geometric analysis, analytic inequalities, approximation theory and optimization, as well as their applications. Many of the chapters are related to the seminal contributions of Th. M. Rassias and are based upon his initial findings