SQL*Plus is the command-line interface to the Oracle database. It exists to let you enter and execute ad hoc SQL statements and PL/SQL code blocks, and, if you're a database administrator (DBA), to issue database administration commands such as STARTUP and SHUTDOWN. This chapter explains what SQL*Plus is, how it relates to the Oracle database, and why you should master it. At the end of the chapter, I'll introduce you to the sample data used for many of the examples in this book. You can load the data and follow along as you read.