JavaScript is widely used for simple online applications. This book presents HTML and JavaScript in a way that uniquely meets the needs of students in the sciences and engineering. It explains how to create simple client-side applications for scientific and engineering calculations. It includes many complete HTML/JavaScript examples with science/engineering applications to guide the reader progressively and comprehensively through the subject. This book is specifically targeted at a technical audience-- but not one that is necessarily familiar with a programming language,-- and gives the reader a sufficient understanding of HTML and JavaScript to write their own online applications. The exposition emphasises basic programming principles in a modern Web-oriented environment, making it also highly suitable for an introductory programming course for non-computer science majors. It is also ideal for self-study. There is supplementary website for this book containing code examples and all graphics files.