There are three non-mutually exclusive reasons to read this book: (i) you love science; (ii) you do science; and/or (iii) you teach science. As a teacher of general chemistry, I have found myself teaching things from modern textbooks that have been (by the year 2000) rehashed many times by generations of textbook authors and college professors. Over the years, much of the detail of history has been lost; some of the important caveats associated with the original research have been stripped away; and the material has become dogmatic.Today, it is hard to believe that in 1900 learned scholars could debate the existence of atoms and molecules. Ironically, if Albert Einstein had done nothing else, his 1905 paperOn the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat. Annalen der Physik 17 (1905): 549-560.would have been regarded as important to proving the existence of molecules, atoms and our modern theory of thermodynamics. Modern textbooks generally do not spend much time discussing how we made this critical passage from the ignorance of 1600 to the enlightenment of 2000; and at one time, I was a strong believer that it was a waste of time to consider the history (complete with personal tribulations, priority disputes, missteps, false starts and general confusion) of scientific study. But I have come to believe that we now accept some ideas as "facts" and have not thoroughly questioned the hypotheses of renowned scientists. In this informal history (compiled largely from popular secondary sources), I am not going to deeply criticize the pathway or results that have been used to construct our modern view of matter and energy, but I did want to give the general reader (and interested student) an outline of how we got here. Hopefully, this approach will convert the pillars of modern chemistry and physics from infallible icons into imperfect people with imperfect hypotheses that we should feel free (indeed, obligated) to question and challenge. Besides that, perhaps looking at how these people came to their discoveries will suggest methods of reasoning and investigation to modern researchers.