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: If you maksat to build a public API, it's better to use IEnumerable than List, because you better use https://garrettvgpwc.wikimillions.com/3250399/benim_c_ienumerable_nerelerde_kullanılıyor_başlarken_Çalışmak