Book excerpt: This book introduces the basic concepts of MathLink and explains how to extend Mathematica using MathLink. Miyaji and Abbott show how to write Mathlink programs and how to apply Mathlink in a variety of situations. MathLink comprises a simple and powerful way to write programs that communicate with Mathematica and offers access to a wide range of network resources. Writing network programs is the most demanded skill in the Internet Age and MathLink provides a sophisticated level of network programming to the nonprogrammer, scientist, engineer, and student. Mathematica's powerful "problem-oriented" programming language includes symbolic and numerical computation, and excellent graphics capabilities, which enables users to write compact and elegant programs that are much shorter than in conventional languages. Within MathLink one can write programs that communicate with Mathematica. Since most electronic devices are connected to, or controlled by, a computer, it is straightforward to interface them to Mathematica. Once your device is connected to Mathematica, you can manipulate the data within Mathematica. The authors examine in detail source code for a range of practical examples ranging from elementary to advanced, allowing readers to easily adapt the code to suit their own practical needs. The text assumes that the reader is already familiar with Mathematica.