Starting in July, 2011, all EU countries will require that your pet have a microchip and all documentation supporting the microchip number to permit entry. Some EU countries will accept all major brands of microchips and others will only accept the 15 digit ISO microchips. If your pet is micro chipped with a microchip other than a 15 digit ISO microchip, it is recommended that you carry your own microchip scanner. Additionally, EU 998 Regulations do not call for blood titre test for pets entering Europe from a third country. Three members of the EU have exemptions from this regulation: UK, Malta, and Sweden. This exemption expires next year and it remains to be seen whether it will be extended.
UPDATE: updated information on bringing your pet to Europe.