Subtle is the Lord: The Science and the Life of Albert Einstein is a biography of Albert Einstein written by Abraham Pais. First published in 1982 by Oxford University Press, the book is one of the most acclaimed biographies of the scientist. This was not the first popular biography of Einstein, but it was the first to focus on his scientific research as opposed to his life as a popular figure. Pais, renowned for his work in theoretical particle physics, was a friend of Einstein's at the Institute for Advanced Study. Originally published in English in the United States and the United Kingdom, the book has translations in over a dozen languages. Pais later released a sequel to the book in 1994 titled Einstein Lived Here and, after his death in 2000, the University Press released a posthumous reprint of the biography in 2005, with a new foreword by Roger Penrose. Considered very popular for a science book, the biography sold tens of thousands of copies of both paperback and hardcover versions in its first year. The book has received many reviews and, the year after its initial publication, it won both the 1983 National Book Award for Nonfiction, in Science (Hardcover), and the 1983 Science Writing Award.

Before becoming a science historian, Pais was a theoretical physicist and is said to be one of the founders of theoretical particle physics. Pais knew Einstein and they developed a friendship over the last decade of Einstein's life, particularly while they were colleagues at the Institute for Advanced Study in Princeton. He drew from this experience when writing the book, which includes several vignettes of their interactions, including a story of his final visit to see Einstein, who was ill and would die a few months later. The Quantum Theory portion of the book was previously published, in similar form, in a 1979 article Pais coauthored in Reviews of Modern Physics.

The book draws its title from a quote by Einstein that translates to "Subtle is the Lord, but malicious he is not". The quote is inscribed in stone at Princeton University, where Einstein made the statement during a 1921 visit to deliver the lectures that would later be published as The Meaning of Relativity. When asked later in life to elaborate on the statement, Einstein said in 1930: "Nature hides its secret because of its essential loftiness, but not by means of ruse." Isaac Asimov summarized this as meaning "the laws of nature were not easy to uncover, but once uncovered, they would not give uncertain result", comparing to another famous Einstein quote: "I cannot believe that God would play dice with the universe".

The book serves as both a biography of Albert Einstein and a catalog of his works and scientific achievements. Though there were several well-known biographies of Einstein prior to the book's publication, this was the first which focused on his scientific research, as opposed to his life as a popular figure. Einstein himself, in 1946 at the age of 67, expressed a desire to be remembered for his work and not his doings, stating "the essential in the being of a man of my type lies precisely in what he thinks and how he thinks, not in what he does or suffers." Beyond the biography, the book serves as the first full-scale exposition of Albert Einstein's scientific contributions; one reviewer noted that, although literature on Einstein is not lacking, prior to this book, someone trying to research Einstein's scientific contributions "faced a choice between reading one or more popularizations of limited scope (and often even more limited depth) and trying to read and digest the almost 300 scientific papers he produced."

Pais explains in the book's introduction that an illustration of Einstein's biography would have his work in special relativity building toward general relativity and his work in statistical physics would build toward his work in quantum theory, and all of them would build toward his work in unified field theory; the book's organization represents his attempt to respect that outline. The book has 31 chapters that are divided into eight major sections, with purely biographical chapters marked stylized with italics. These italicized chapters present a non-technical overview of Einstein's life, while the bulk of the book explores Einstein's contributions in mathematical detail. The first part of the book, titled Introductory, serves as a quick summary and outline of the book's contents. The second section, on statistical physics, includes Einstein's contributions to the field between 1900 and 1910 as well as a discussion of the probabilistic interpretation of thermodynamics. The third section, on special relativity, describes the history of special relativity and Einstein's contributions early to relativity theory as well as their relation to the work of Henri Poincaré and Hendrik Lorentz. The next section, on general relativity, covers Einstein's developments of the theory from around 1907 to 1915 and the development of the universally covariant gravitation field equations. The chapter also includes discussion on the development of general relativity by other scientists from 1915 to 1980. Section six includes a biography chapter on Einstein's later life and a discussion of his work in unified field theory. The final section, section six on quantum theory, covers Einstein's work in the field extending over his entire career.

The book received critical acclaim upon its initial release and was subsequently translated into fifteen languages, establishing Pais as an internationally renowned scholar in the subject. There were many reviews of the book, including articles published in magazines including Scientific American, The Christian Science Monitor, and The New York Review of Books, as well as newspaper articles published in The New York Times, The Los Angeles Times, The Leader-Post, The Observer, The Age, The Philadelphia Inquirer, The Santa Cruz Sentinel, and The Arizona Republic.

The book has received favorable mentions in reviews of other works and papers discussing the history of Einstein's contributions. Of the reviews of the 1994 sequel, Einstein Lived Here, Engelbert Schücking wrote that the original biography was "magisterial" and Roger Highfield opened his review of the new volume with: "Among my collection of books on Einstein, there is a dog-eared copy of... Subtle is the Lord. Its poor condition pays tribute to the value of this brilliantly researched book". Bruno Augenstein wrote in 1994 that the book was a "definitive" scientific biography of Einstein. Schücking, in a 2007 review of the book Einstein: His Life and Universe by Walter Isaacson, stated that "the wonderful book by Pais, which was republished by Oxford University Press in 2005, with a preface by Roger Penrose, is still the best introduction to Einstein’s physics." Similarly, a 2005 article discussing "Einstein's quest for unification" by John Ellis opened by stating that the book is the "definitive scientific biography of Einstein" and that it "delivered an unequivocal verdict on Einstein's quest for a unified field theory".

On the book's release in 1982, John Stachel wrote a positive review of the book that stated the book gives a detailed account of nearly all of Einstein's significant scientific contributions along with historical context from an "eminent physicist's perspective". Stachel went on to say that the biography sections "constitutes the most accurate account of Einstein's life yet written" and that the book is "both unique and indispensable for any serious Einstein scholar". He closed the review by saying the book would "serve not only as a source of profound insight and pleasure to many readers but as a further spur to the current renaissance of Einstein studies". In a second 1982 review, John Allen Paulos wrote that it "is a superb book.". Banesh Hoffmann reviewed the book in 1983 calling it "outstanding" and that it is a "lively book" and a "major contribution to Einstein scholarship". Isaac Asimov wrote that the book gives a "concise history of the physics involved" and that it is "engagingly written". William Hunter McCrea wrote a critical review of the book in 1983, taking issue with several of Pais' statements, but wrote that overall, it was "a major work on Einstein" and that "[f]or those who know well what Einstein achieved, but who may have wondered how he did it, this book should tell them almost all they can ever hope to learn." A third 1983 review stated that the book is a "superb biography of Einstein" and was likely to "become required reading for anyone interested in the history of 20th century physics". The book was also reviewed in German that same year.