A First Course in string Theory gives a self-contained explanation of string theory at a level that is truly understandable to advanced undergraduates, beginning graduate students, and physicists in all areas of research. Dealing with string theory in two parts, the book first covers the classical and quantum dynamics of relativistic strings and gives a brief introduction to superstrings. The second part covers D-branes, string thermodynamics, and various aspects of T-duality. It also discusses possible physical applications : the Standard Model on D-branes, the calculation of the entropy of black holes, and the string-theory/gauge-theory correspondence. With more than 150 problems and 100 exercises, this book is ideal for introductory courses in string theory, as well as for self-study. Solutions to the problems are available to lecturers and teachers via firstname.lastname@example.org.