Dictionary provides a mapping between a key and a single value, and is one of the most used collection types in the .NET Framework. Programs often need a mapping between one key and multiple values. Today we’re releasing an experimental NuGet package with a new related type, MultiDictionary. The MultiDictionary is a simple, intuitive collection that essentially functions like a Dictionary> but abstracts the ICollection. A more precise definition is that it is a Dictionary that allows multiple TValues to be added for any TKey (i.e. keys don’t have to be unique).