Suitable for graduate students in physics and mathematics, this book presents a concise and pedagogical introduction to string theory. It focuses on explaining the key concepts of string theory, such as bosonic strings, D-branes, supersymmetry and superstrings, and on clarifying the relationship between particles, fields and strings, without assuming an advanced background in particle theory or quantum field theory, making it widely accessible to interested readers from a range of backgrounds. Important ideas underpinning current research, such as partition functions, compactification, gauge symmetries and T-duality are analysed both from the world-sheet (conformal field theory) and the space-time (effective field theory) perspective. Ideal for either self-study or a one semester graduate course, A Short Introduction to String Theory is an essential resource for students studying string theory, containing examples and homework problems to develop understanding, with fully worked solutions available to instructors.