Isaac Newton, like Albert Einstein, is a quintessential symbol of the human intellect and its ability to decode the secrets of nature. Newton's fundamental contributions to science include the quantification of gravitational attraction, the discovery that white light is actually a mixture of immutable spectral colors, and the formulation of the calculus. Yet there is another, more mysterious side to Newton that is imperfectly known, a realm of activity that spanned some thirty years of his life, although he kept it largely hidden from his contemporaries and colleagues. We refer to Newton's involvement in the discipline of alchemy, or as it was often called in seventeenth-century England, "chymistry." Newton wrote and transcribed about a million words on the subject of alchemy. Newton's alchemical manuscripts include a rich and diverse set of document types, including laboratory notebooks, indices of alchemical substances, and Newton's transcriptions from other sources.