This story is about the fundamentals of web2.0 theory and the added value of APIs (application programming interfaces) for modern businesses, developers and software consumers The first 80 slides (about the fundamentals of web2.0) are available as a separate slidedeck via http://www.slideshare.net/OlafJanssenNL/part-1-of-the-lecture-so-you-think-you-understand-everyday-life-web20-api-theory-still-very-relevant-in-2013 The second part of the story - i.e. this particular slidedeck - deals with API-fundamentals and shows how APIs are the cornerstones of modern business development (BizDev2.0). By looking at casestudies from Google Maps, Twitter, Amazon, eBay, Moo, Flickr, Netflix and other web2.0-companies, it becomes clear how APIs add value for all parties on the modern web. This presentation was given by Olaf Janssen - Product & Services Advisor for the National Library of the Netherlands (KB) - as a lecture for students of the master's course "Digital Access to Cultural Heritage" at Leiden University on 7-3-2013