How do ByVal and ByRef behave when a VB.NET parameter refers to an object?

ByVal copies the argument value into the parameter. For a reference type, that value is a reference, so the method can still mutate the same object, but reassigning the parameter does not replace the caller’s variable. ByRef allows the method to replace the caller’s variable as well. For value types, ByVal normally copies the value. Prefer retu ing a result or clear object methods when that makes changes easier to follow. Do not claim ByVal makes an object immutable or creates an independent deep copy.