Shaheed Bhagat Singh’s ‘Jail Notebook’ opens a window into his exploration of ideas of distinguished thinkers and philosophers. Well-known among his comrades as an avid and voracious reader, Bhagat Singh managed to procure during his imprisonment in jail a large number of selected books by prominent authors of his choice. The excerpts, notes and quotes from those books which he wrote down in his jail notebook reflected not only the seriousness with which he studied the books but also his intellectual sophistication and social and political concerns. However, the perfunctory reference to the sources or books from which these notes and quotes were taken left a rather perplexing question mark with regard to the authentic source i.e. from exactly which editions of which books by which particular authors were these taken. As a result, fantastic claims and wild speculations came to be made by admiring scholars as to the number of books and the kind of original works of great thinkers that Bhagat Singh was able to study in the jail. As a sequel to that the present work Bhagat Singh’s ‘Jail Note Book’, Its Context and Relevance by Harish Jain represents an exceptionally tenacious and laborious search and research into the specific and authentic sources of the particular notes and quotes entered in the Jail Notebook. The story of the author’s exploration for over a decade, searching and identifying books by following astute guesses and hunches, and rummaging through many likely or probable books accessible at that time, many of which were not easily available now, makes a fascinating reading. Contextualising the importance and reach of the ideas of the various authors in those times helps one to understand why they might have appeared significant to Bhagat Singh. Besides discussing the ideas central to the books he read attempt has been made here to explain the import of the quotes he chose to copy. A unique work of its kind, this study is both enriching and a pleasure to read.