Backbone VirtualCollection allows you display a subset of a Backbone collection in a Backbone view that updates in real time. It works great with Marionette CollectionViews. If you're thinking "why don't you just place the models you're interested in a new collection?" the answer is that the new collection won't update itself when new models are added to the original collection, so you're creating data inconsitency. That's why we need a VirtualCollection.