This book grew out of a course that I taught at the Saha Institute of Nuclear Physics more than once. At this institute, where I worked until my retirement in 2017, students entered after doing theirMSc courses. Therefore, the level of thematerial of the book is appropriate for students at that level, or even for students doing their MSc in Physics.

Although the course I taught was called ‘Mathematical Physics’, I did not really delve into Physics very much. I stuck to the mathematical tools necessary for a physicist, and only indicated where and why they might be applicable in Physics. I maintained the same philosophy during the writing of the book.

Not everything contained in the book was presented in the class. A one-semester course cannot possibly accommodate everything that is there in the book. If anyone else wants to teach a course based on this book, he/she will have to choose chapters that should be covered in the course, leaving the other chapters for further study material.

It took me several years to write the book. As I now look back at it, I see that I haven't been able to maintain a uniform writing style. In some parts of the book, the reader will find definitions that appear within the running text of the paragraphs, whereas in some other parts the definitions are highlighted as separate paragraphs, and numbered. There are other similar irregularities. I apologize for this uneven style.

I never understood the difference between the words ‘theorem’, ‘lemma’ and ‘proposition’ as applied in mathematical texts. So all statements that require a proof have been termed ‘theorem’ in my book.

During the time that I taught the course and later when I wrote most parts of the book, I have been extremely fortunate to have many friends around from whom I have learned a great deal. The list of names include Atish Bagchi, Bireswar Basu-Mallick, Pritibhajan Byakti,Amitabha Chakrabarti, David Emmanuel-Costa,Anindya Datta, Daniel Kornhauser, Arnab Kundu, Indrajit Mitra, Shibaji Roy, Ashoke Sen — and is by no means exhaustive. I am grateful to all of them.