The Scala IDE for Eclipse is best installed (and updated) directly from within Eclipse.
First follow the navigation path "Help → Software Updates ... → Available Software" then click the "Add Site..." button.
All update sites for installation are at http://download.scala-ide.org/. The constellation of versions can be daunting at first. Read this paragraph to make an informed choice.
The Eclipse plugin comes with a Scala compiler and Scala library. In a given Eclipse installation there can be a single version of the Scala plugin for Eclipse, so you need to decide what Scala version you are going to use. In other words, the choice of Scala version (2.8.x, 2.9.x, etc) is not per project, but per Eclipse installation.
Scala IDE for Eclipse supports three versions of the Scala compiler:
Once you decided for the Scala version, you need to choose a version of the IDE.
Check http://download.scala-ide.org/ for all downloads.
You have successfully installed the Scala plugin, and you are eager to try it out on your favorite project. Please take the time to read the following paragraphs, which should help setting up your development environment quickly and without pain.
Important: Before you begin, make sure your Scala sources follow the Java convention for packages. Each package should appear in its own directory with the same name. Eclipse expects this convention to be followed when it looks for classes.
SBT is the standard build tool for Scala projects. There are two versions in wide use today: 0.7.x and 0.10+. Both have plugins that can generate Eclipse project files out of the SBT project definition.
Once you have installed and generated the Eclipse project files using one of the above plugins, start Eclipse and Choose File/Import, then choose Existing Project into workspace. Navigate to the directory of your project, and Eclipse should detect the generated project.
Important: SBT manages the dependency to scala-library.jar. Make sure the version of Scala you use in your SBT project matches the version of Scala installed in Eclipse.
The number one cause of nothing works is a mismatch between the Scala version of the Eclipse plugin and your project's. Make sure there is only one version of the Scala library on your classpath (prime suspect is Maven Dependencies, which can download and add an incompatible
You can also the Known Issues page.