The document discusses building mobile apps using HTML, CSS, and JavaScript. It covers the staggering growth of mobile usage statistics. It then discusses the fragmentation challenges posed by different mobile platforms and devices. It presents three approaches for building mobile apps: pure native apps, web apps, and hybrid apps that combine web technologies with native platforms. The rest of the document outlines best practices for designing mobile-friendly interfaces and building offline and device API-enabled web apps using technologies like PhoneGap.