An International Driving Permit IDP is proof in nine languages that you hold a valid drivers licence in your home country.

• IDP's are officially sanctioned by the United Nations
  and accepted worldwide (in over 150 countries) as a recognised form
  of identification.
• Your IDP carries your identification details in nine
  languages (Arabic, Chinese, English, French, German, Italian, Russian,
  Spanish & Swedish), in case you need to communicate with foreign
  authorities.
• An IDP is proof that you hold a valid drivers licence in you home
  country at the date of issue of the IDP and should be carried with
  your domestic driver's licence.

Do I need one?

• IDP's are a special permit for tourists, authorised by the United Nations Treaty for the purpose of allowing motorists to drive internationally without further tests of applications provided their domestic driver's licence is valid.
• An IDP is a requirement for renting a vehicle in many countries.
• In some countries you may be asked to surrender
  your passport under certain circumstances. An IDP provides an extra
  photo ID in nine languages which you can always carry with you.
• An IDP provides inexpensive additional security.

Which countries require an IDP?

• Contact you state Automobile association eg NRMA, RACQ, RACT, RACV etc - visit their web sites for application forms and details about which countries require an IDP.