AOL will promote the iTunes store to its European users and provide a channel for user registration. Links to iTunes artists, albums and songs will appear throughout the AOL Music channel.
The service's debut comes just weeks after European digital download services were unveiled by Napster and Sony Connect, a joint venture between the electronics giant and McDonald's.
Separately, Coca-Cola this week revealed that its Mycokemusic.com service has sold 500,000 downloads in the first six months of operation.
Competition in the market has become fierce in recent months. Charities Oxfam and War Child are offering music downloads, and HMV, Virgin and MSN are all relaunching their existing services.
In the battle to win consumers, distribution will become a key factor.
Napster, a unit of US media company Roxio, this week announced a partnership with NTL to offer subscriptions to the UK cable group's 1m broadband customers.
Apple is expected to charge 99p a track, which would match its rivals.
In the US, Apple sells tracks for 99 cents.