You're doing more work though. You're converting to a List<T> (in order to caox the lazy enumerable to enumerate). You should use Aggregate for a more (genera

You're doing more work though. You're converting to a List<T> (in order to caox the lazy enumerable to enumerate). You should use Aggregate for a more (generalised) way to reduce/fold collections into a value: var sum = arr.Aggregate(0, (t, x) => t + (x * x)); On the whole though it's better to use Linq until it's not. It's more declarative which will lead to more reliable code. Optimise when you find performance issues, don't write bad code just because you may gain a few nanoseconds here and there.