This book contains three contributions with topics in dynamical systems: Limit relative category and critical point theory, coexistence of infinitely many stable solutions to reaction diffusion systems, and second-order hyperbolic mixed problems. All the authors give a careful and readable presentation of recent research results, which are of interest to mathematicians, mathematical biologists, chemists and physicists. The book is written for graduate students and researchers in these fields and it is also suitable as a text for graduate level seminars in dynamical systems.