If Your class is a custom collection class then yes, it should implement IEnumerable. In this case a public property for the inner list would be redundant. Imagine a simple class: Down Below I took part of a code I was looking at. I don't understand the IEnumerable part of https://claytonsfnvb.dailyblogzz.com/28538037/the-ultimate-guide-to-c-ienumerable-nasıl-kullanılır