Killed in action at Gallipoli in the Dardanelles Campaign of 1915, aged just twenty-seven, Henry Gwyn Jeffreys Moseley was widely regarded as the most promising British physicist of his generation. His pioneering measurements of X-ray spectra provided a firm basis for the concept of atomic number and re-cast the periodic table of the elements into its modern form. Had he survived, he seemed destined to win a Nobel Prize. This book is a commemoration of Moseley's life, work, and legacy. Inspired by the exhibition 'Dear Harry... Henry Moseley: A Scientist Lost to War', at the Museum of the History of Science, Oxford, in 2015-2016, and revisiting earlier accounts, thirteen historians and scientists chart his experience of Manchester and Oxford; his military service; the reception of his work by the scientific community; and the impact of his work upon X-ray spectroscopy in physics, chemistry, and materials science. For Science, King & Country speaks to those with an interest in history, science, and the First World War, and draws upon a wealth of archives, artefacts, and recent research on the reward systems of science. Overall, it presents a comprehensive account of a young scientist whose brief but mercurial career paved the way to a new understanding of nature, and to shaping the future of physical science.