The Cryptoclub: Cryptography and Mathematics Afterschool and Online is a five -year project designed to introduce middle school students across the country to cryptography and mathematics. Project partners include the Young Peoples Project (YPP), the Museum of Science and Industry in Chicago, and Eduweb, an award-winning educational software design and development firm. The intended impacts on youth are to improve knowledge and interest in cryptography, increase skills in mathematics, and improve attitudes towards mathematics. The secondary audience is leaders in afterschool programs who will gain an increased awareness of cryptography as a tool for teaching mathematics and adopt the program for use in their afterschool programs. Project deliverables include online activities, online cryptography adventure games, interactive offline games, a leader's manual, and training workshops for afterschool leaders. The project materials will be developed in collaboration with YPP staff and pilot tested in Year 3 at local afterschool programs and YPP sites in Chicago in addition to four national sites. Field testing and dissemination occurs in Year 4 at both local sites in Chicago and national locations such as afterschool programs, science centers, and community programs. Six 3-day training workshops will be provided (2 per year in Years 3-5) to train afterschool leaders. It is anticipated that this project will reach up to 11,000 youth, including underserved youth in urban settings, and 275 professional staff. Strategic impact resulting from this project includes increased awareness of cryptography as a STEM topic with connections to mathematics as well a greater understanding of effective strategies for integrating and supporting web-based and offline activities within informal learning settings. The Cryptoclub project has the potential to have a transformative impact on youth and their understanding of cryptography and may serve as a national model for partnerships between afterschool and mentoring programs.