Just as with Java, in Scala you can put bounds on the generic types allowed to a generic class or method.

Suppose we have an object hierarchy of entities. We have a root entity that all must extend, and then a special secondary entity for reference data (data that is a code and a description and only aggregated by other entities).

Further, we wish to define a sorting class that we can apply to all reference data.

We could have created the sorter class to just take reference data entities, but the regular and sorted methods would not return properly typed Lists, they would return lists of our reference data root class and not, say List[Gender], which would be more useful.

This is essentially the same concept as List<T extends Foo> that you have in java, though more concise (at the cost of clarity, IMO).

You can also bound the other way, however I have yet to come up with a usable example of this.