Codemasters will continue operating LotRO until June 1st of this year, after which "Turbine is taking over full operations of The Lord of the Rings Online throughout Europe starting June 1, 2011. We're merging the US and EU services into one mega-service we're calling the LOTRO Global Service."
This summary is at the head of a combined announcement and FAQ Turbine has provided to answer any questions players might have. A long list of those has been anticipated and answered, such as how EU players will migrate their accounts, whether characters and inventory will be affected, whether VIP and Lifetime accounts will be changed, and so on. You can check out all the details on Turbine's official announcement page.