Information about tourism to and within Europe is available from a variety of sources:

ETC Factsheet on Tourism in Europe (September 2009)

National Statistical Offices in Europe
A list of statistical sources in ETC member countries on international and domestic tourism to and within their region.

  
'TourMIS' - European Tourism Statistics
TourMIS* gives you easy access to data on tourism flows between and to the majority of the 39 European countries.  You can obtain free registration to the database via the above link. 
(*TourMIS - the Tourism Marketing Information System is a database of the Austrian National Tourist Office & the Institute for Tourism and Leisure Studies (University of Vienna) in collaboration with ETC ).

ETC New Media Trend Watch (statistics on the online market)
The most comprehensive source of statistics on the online travel market and use of the internet and e-commerce for travel & tourism - on a country by country basis.

Statistics on the major Long-Haul Markets 
Statistics on outbound travel from Europe's primary source markets: 
Australia, Canada, China, Japan, Latin America, USA.

Our Market Insights also provide statistical data on the following markets:  
Australia, Brazil, Canada, China, India, Japan, Mexico,  Russia, S. Korea, Thailand, UAE, USA,

International Tourism Organisations:
A list of links to other sources of data on international tourism.

ETC Research Reports & Studies: 
Gives you access to a wide range of Research & Reports published by the ETC.