If I cared what the order was, I'd expect that I'd have to order it myself, e.g.: var foo = things.SelectMany(thing=>thing.SubThings).OrderBy(subthing=>subth

If I cared what the order was, I'd expect that I'd have to order it myself, e.g.: var foo = things.SelectMany(thing=>thing.SubThings).OrderBy(subthing=>subthing.PropertyICareAbout) Particularly if things is some interface that I don't know the details of, like IEnumerable, ICollection or IDictionary.