This proceedings volume gathers together selected, peer-reviewed works presented at the Polynomial Rings and Affine Algebraic Geometry conference which was held at the Tokyo Metropolitan University on February 12-26, 2018, in Tokyo, Japan. In this book, the reader will find some of the latest research conducted by an international group of experts in affine and projective algebraic geometry. Topics covered include group actions and linearization, automorphism groups and their structure as infinite-dimensional varieties, invariant theory, the Cancellation Problem, the Embedding Problem, Mathieu spaces and the Jacobian Conjecture, the Dolgachev-Weisfeiler Conjecture, classification of curves and surfaces, real forms of complex varieties, and questions of rationality, unirationality, and birationality. The articles contained in this volume will be of interest to all researchers and graduate students working in the fields of affine and projective algebraic geometry, as well as in certain aspects of commutative algebra, Lie theory, symplectic geometry and Stein manifolds.