How do I know whether my car is OBD-II compliant?

1996 or newer model year vehicle sold in the United States

2001 or newer model year gasoline vehicle sold in the European Union

8.1. Vehicles with positive-ignition engines
With effect from 1 January 2000 for new types and from 1 January 2001 for all types, vehicles of category M1, except vehicles the maximum mass of which exceeds 2500 kg, and vehicles of category N1 class I, must be fitted with an on-board diagnostic (OBD) system for emission control in accordance with Annex XI. [...]

2004 or newer model year diesel vehicle sold in the European Union

8.2. Vehicles with compression-ignition engines
Vehicles of category M1, except
- vehicles designed to carry more than six occupants including the driver,
- vehicles whose maximum mass exceeds 2500 kg,
from 1 January 2003 for new types and from 1 January 2004 for all types, must be fitted with an on-board diagnostic (OBD) system for emission control in accordance with Annex XI.

Other vehicles