The CK-12 Foundation is a California-based non-profit organization which aims to increase access to low-cost K-12 education in the United States and abroad.

[5] Teacher-generated content was initially made available under Creative Commons Attribution licenses so as to make it simpler, easier, and more affordable for children to access educational resources.

[12] The foundation's FlexBook website permits the assembly and creation of downloadable educational resources, which can be customized to meet classroom needs.

Content is offered under a Creative Commons license, removing many of the restrictions that limit distribution of traditional textbooks, and are available in various formats.

As of 2012, some 5,000 individual elements were available in various formats such as textual descriptions, video lectures, multi-media simulations, photo galleries, practical experiments or flash cards.