sbt - short for Simple Build Tool, is the most popular build tool for Scala applications. After using the Scala REPL for a while, you will want to start building simple applications that involve writing the code once and running it over and over again. This is where sbt comes in. You can use it to build your code into a complete application, ready to run. How to use sbt is outside the scope of this course, but we are including instructions so you will have it when you are ready to explore Scala further.