This book is the proceedings of the conference on Arrangements of Hyperplanes, held in August 2009 as the 2nd Mathematical Society of Japan Seasonal Institute. The modern study of arrangements of hyperplanes started in the early 1980s. Since the object of study is simple (just a finite set of hyperplanes), there are various mathematical approaches to arrangements including algebra, topology, combinatorics, singularities, integral systems, hypergeometric functions, and statistics. Since numerous world-renowned experts gave talks at the 2nd MSJ-SI, this book covers many pioneering approaches and new topics in the theory of arrangements as well as indispensable classical results. The book is recommended to any researcher or graduate student interested in arrangements of hyerplanes.