This video module presents an introduction to cryptography – the method of sending messages in such a way that only the intended recipients can understand them. In this very interactive lesson, students will build three different devices for cryptography and will learn how to encrypt and decrytp messages. There are no prerequisites for this lesson, and it has intentionally been designed in a way that can be adapted to many audiences. It is fully appropriate in a high school level math or computer science class where the teacher can use it to motivate probability/statistics or programming exercises. The video module itself should take one class session, although the building of the cryptography devices may take longer and could be done ahead of time. Materials necessary for this lesson include paper cups, scissors, tape or glue and pens or pencils. Additional materials are downloadable from this website. During the in-class portion of this interactive lesson, students will learn to build the cryptography devices and will learn how to send and “crack” secret messages.