Scala collections are a well-understood and frequently-used programming abstraction that can be distinguished between mutable and immutable collections. Like a mutable variable, a mutable collection can be changed, updated, or extended when necessary. Like an immutable variable, immutable collections; cannot be changed. Most collection classes that utilize them are located in the packages scala.collection, scala.collection.immutable, and scala.collection.mutable, respectively.

The following hierarchical diagram (Figure 1) shows the Scala collections API hierarchy according to the official documentation of Scala. These all are either high-level abstract classes or traits. These have mutable as well as immutable implementations.