Horse's mouth:

Key points of the Schengen acquis...

1. Citizens of countries fully implementing the Schengen acquis (see below) may enter such countries anywhere without any checks.
2. Third-country nationals who have been granted a visa with no territorial restrictions (visitor's or business visa allowing the holder to stay up to 90 days per six-month period, transit or airport visa) by a country fully implementing the Schengen acquis (see below) may, for the duration of the visa's validity, enter any other fully implementing country for the same purpose and also without checks.
3. Third-country nationals with a residence permit valid in one fully implementing country may travel on a valid passport, without requiring a visa, for up to 90 days per six-month period to any other fully implementing country; they are also not subject to border checks at the Schengen area's internal borders.
4. Harmonized visa policies of Schengen countries (common list of third countries whose nationals require visas).
5. External border checks according to a common Schengen standard.
6. Access by all Schengen countries to the Schengen Information System (SIS), which provides data on persons and objects throughout the Schengen area especially in connection with inquiries by police and judicial authorities.
7. Close police and judicial cooperation.
8. Joint efforts to combat drug-related crime.
9. Rules determining competence for asylum procedures, now replaced by Council Regulation (EC) No. 343/2003 of 18 February 2003 (so-called Dublin II Regulation).

Doesn't get much clearer than that
Best to get writing apologetically A.S.A.P., as previously suggested...
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