Over the last decade or so, we're seeing the emergence of a new form of scale. Today's massively scaling startups - which rapidly grow to millions of users and billions in valuation - do not sell a product or service. Instead, they build a platform on which others can create and exchange value.The many manifestations of the platform business model - social media, the peer economy, cryptocurrencies, APIs and developer ecosystems, the Internet of things, crowdsourcing models, and many others - are becoming increasingly relevant.Yet, most new platform ideas fail because the business design and growth strategies involved in building platforms are not well understood.Platform Scale lays out a structured approach to designing and growing a platform business model and addresses the key factors leading to the success and failure of these businesses.