This book is a complete guide to the use of Dyalog APL describing a large number of common coding techniques, and discussing a variety of interfaces, including file handling and COM/OLE. It provides a thorough introduction to developing Graphical User Interfaces in Dyalog APL and wraps up with an overview of the publishing tool NewLeaf and the RainPro graphics engine, two of the powerful tools that are included with Dyalog APL. The book is aimed at helping new users get started with Dyalog APL and advancing them to a point where they can produce working solutions by expressing ideas directly in APL. Step by step, this book gives the reader a thorough grounding in the philosophy of the APL language, and the many examples illustrate the practical capabilities of this dynamic software development environment. Each chapter ends with a set of exercises on which beginners and advanced readers can test their skill as they progress through the course. Solutions with detailed explanations are given in the last chapter. Exercises and examples are supplemented by a set of companion files containing sample programs and data, which can be downloaded from the Dyalog web site. Although the book is primarily aimed at new developers and is suitable for students with no prior programming experience, most chapters end with a "Specialist's Section" containing tips and tricks which will be of interest to readers who do have experience with programming - and some prior knowledge of APL. Dyalog APL - the most widely used APL development platform available - is used in research and business applications where it is important to integrate domain experts in the software development process. Dyalog APL allows rapid prototyping of both simple and complex processes, and is especially strong where solutions have an analytical or mathematical component. Without recoding, these solutions can be used to power secure, high performance solutions with thousands of simultaneous users.