These slides accompanied the OER Research Hub webinar "The Impact of Open Textbooks in the USA and South Africa: When? Why? How?" on 28 May 2014. Speakers: Megan Beckett (Siyavula), Beck Pitt (The Open University, OER Research Hub) and Daniel Williamson (OpenStax College). The session was chaired by Martin Weller (The Open University, OER Research Hub). You can watch a recording of the webinar here: http://tinyurl.com/p926br2