Jacques Hadamard, among the greatest mathematicians of the twentieth century, made signal contributions to a number of fields. But his mind could not be confined to the upper reaches of mathematical thought. He also produced a massive two-volume work, on plane and solid geometry, for pre-college teachers in the French school system. In those books, Hadamard's style invites participation. His exposition is minimal, providing only the results necessary to support the solution of the many elegant problems he poses afterwards. That is, the problems interpret the text in the way that harmony interprets melody in a well-composed piece of music. The present volume offers solutions to the problems in the first part of Hadamard's work (""Lessons in Geometry. I. Plane Geometry"", Jacques Hadamard, Amer. Math. Soc. (2008)), and can be viewed as a reader's companion to that book. It requires of the reader only the background of high school plane geometry, which ""Lessons in Geometry"" provides. The solutions strive to connect the general methods given in the text with intuitions that are natural to the subject, giving as much motivation as possible as well as rigorous and formal solutions. Ideas for further exploration are often suggested, as well as hints for classroom use. This book will be of interest to high school teachers, gifted high school students, college students, and those mathematics majors interested in geometry.