The article introduces an undergraduate-level textbook on cryptography, titled 'The Joy of Cryptography', which covers the fundamentals of provable security. The book is available online under a Creative Commons license and is supported by the National Science Foundation and the Open Textbook Initiative at Oregon State University. The textbook covers various topics in cryptography, including unconditional cryptography, pseudorandomness, symmetric-key encryption, and asymmetric-key cryptography. The book aims to provide a comprehensive introduction to cryptography for students.