Depends on where. Some countries recognise our licence, but can
only be used for 6 months at the most (you need to confirm the
duration...). If you intend to use it longer than that, or if the
country does not recognise our licence, you need to appy for an
international permit.
Note: it's an international driving PERMIT, not international
licence (no such thing as an international licence). In other
words, you still need to carry your licence with you in case you're
stopped. The permit alone in not enough. 
