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There are misconceptions that all Open Textbooks are "low quality" materials because they are free, but most do undergo a peer review process. The following links describe some of the evaluation criteria to which open textbooks are subject:
The BC Campus Open Textbook Project is Canada's first government-funded project of its kind, and has been tasked with the ongoing creation of open textbooks for the province’s public post-secondary system. The texts are available for free online or through low-cost print versions. BC Campus provides updated lists of these textbooks as more become available.
A non-profit Rice University initiative offering students free textbooks that meet scope and sequence requirements for most courses. Peer-reviewed texts written by professional content developers. Adopt or modify texts, and print-on-demand at cost.