This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, IComparable.CompareTo(object), that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. The instance's IComparable implementation is called automatically by methods such as Array.Sort(Array) and ArrayList.Sort.

The implementation of the IComparable.CompareTo(object) method must return an int that has one of three values, as shown in the following table.

All numeric types (such as int and double) implement IComparable, as do string, char, and DateTime. Custom types should also provide their own implementation of IComparable to enable object instances to be ordered or sorted.