In this chapter we first discuss the installation of SPICE OPUS (for both Linux and Windows). We will go through the startup sequence and the command line options. After that, we will embark on a journey through the most important features of the SPICE OPUS simulator. They include the outline of the input file format, interactive interpreter, all types of analysis, and the built-in scripting language NUTMEG. These features will be illustrated through a simple example (a bipolar junction transistor amplifier). For readers with a circuit analysis background (the enigmatic matrix and circuit model business), we provide circuit models for all kinds of analysis in SPICE.