The present work starts with a condensed biographical account of Bohr’s life and scientific career,from his birth in Copenhagen in 1885 to his death in the same city 77 years later. It then proceeds with a chapter outlining earlier ideas of atomic structure and tracing Bohr’s route from his doctoral dissertation in 1911 over his stays in Cambridge and Manchester to the submission in April 1913 of the first part of the trilogy. The reproduction of Bohr’s five articles is followed by notes and comments directly related to the texts, with the aim of clarifying some of the textual passages and to explicate names and subjects that may not be clear or well known. The reception of Bohr’s radically new theory by contemporary physicists and chemists is discussed in a final chapter, which deals with the immediate reactions to Bohr's theory 1913-1915 mostly among British, German and American scientists. Historians of science have long been occupied with Bohr’s atomic theory, which was the subject of careful studies in connection with its centenary in 2013. The present work offers an extensive source-based account of the original theory aimed at a non-specialist audience with an interest in the history of physics and the origin of the quantum world. In 1922 Bohr was awarded the Nobel Prize for his theory. The coming centenary will undoubtedly cause an increased interest in how he arrived at his revolutionary picture of the constitution of atoms and molecules.