“Each chapter contains an extensive set of exercises, making the book suitable for students interested in an introduction to q-series, elliptic functions, and modular forms without necessarily requiring the theory of modular forms as a prerequisite. … it will be a valuable reference book on Ramanujan’s theta function identities together with their modern extensions and applications.” (Jeremy Lovejoy, Mathematical Reviews, April, 2018)“This is a big and bountiful book, clearly written as a labor of love, and well worth the effort (both of writing and reading it). The book is pitched at advanced undergraduates, graduate students, and professionals or researchers, and this is entirely consonant with this kind of number theory … . It’s been a long time since I visited this material, but I am very happy to see it again.” (Michael Berg, MAA Reviews, November, 2017)