Immutable Collections are a new set of immutable types for .NET. We covered the high level aspects of this new technology a few months back when Erik Meijer interrogated (in his friendly way) the PM of the project, Immo Landwerth, and the lead developer, Andrew Arnott. Since this time, they have received a lot of feedback (thank you!) and have also been busy refining and optimizing their code. Here, Andrew and Immo go deep into how this stuff works and why it's designed the way it is. We talk about how to use these new types and how not to. We learn what the team has been working on and may work on for future releases. As is the case with any Going Deep episode, this is long form conversation and, well, deep. Tune in!More on Immutable Collections (download the preview versions via NuGet): The NuGet package preview includes these types: ImmutableStack ImmutableQueue ImmutableList ImmutableHashSet ImmutableSortedSet ImmutableDictionary ImmutableSortedDictionary Interfaces for each of these types are also defined to facilitate exchange of immutable collection types that may be implemented differently to optimize for very specific performance or memory requirements. See Andrew's blog for more detailed information (on immutable types for .NET and more. Lots of great info...).