Mingxin Wang received his PhD from the Beijing Institute of Technology. He is a prolific educator and researcher in the theory of partial differential equations. In the last two decades, he has made significant contributions to the study of diffusive systems arising in mathematical biology, especially population dynamics. Peter Y. H. Pang received his PhD from the University of Illinois at Urbana-Champaign. His research interests include partial differential equations and geometric analysis. In the past two decades, he has focused on parabolic and elliptic equations with applications in mathematical biology. The two authors have collaborated over a period of more than 15 years, and have co-authored 17 research papers. This book draws upon some key findings and examples resulting from this fruitful collaboration.