Our current concept of matter, one of scientific research's greatest successes, represents a long journey, from questions posed during the birth of philosophy in Ancient Greece to recent advances in physics and chemistry, including Quantum Physics. This book outlines that journey. The book has three parts, each detailing a phase of the journey. The first saw the development of a conception based on "classical" physics; the second saw the construction of the "old" quantum theory attempting to explain the mysterious properties of matter, resulting in formulation of the "new" quantum theory; the third saw the formation of the modern conception of matter, based on quantum mechanics. Along the way, various topics are discussed, including: rediscovery and appropriation of antiquity by Western culture in the modern era; the subsequent revision process in the 16th and 17th centuries and the new experiments and theories of the 18th; attempts to understand the mysterious properties of matter that could not be explained by classical physics; the first quantization hypotheses; discovery of new purely "quantum-mechanical" properties of matter; and the ultimate clarification of atomic structure. This book is aimed at anyone who wants a clear picture of how we arrived at the modern conception of matter.