Who Gave You the Epsilon? is a sequel to the MAA bestselling book, Sherlock Holmes in Babylon. Like its predecessor, this book is a collection of articles on the history of mathematics from the MAA journals, in many cases written by distinguished mathematicians (such as G H Hardy and B. van der Waerden), with commentary by the editors. Whereas the former book covered the history of mathematics from earliest times up to the eighteenth century and was organized chronologically, the 40 articles in this book are organized thematically and continue the story into the nineteenth and twentieth centuries. The topics covered in the book are analysis and applied mathematics, Geometry, topology and foundations, Algebra and number theory, and Surveys. Each chapter is preceded by a Foreword, giving the historical background and setting and the scene, and is followed by an Afterword, reporting on advances in our historical knowledge and understanding since the articles first appeared.