http://www.russell.com/indexes/membership/Reconstitution/Reconstitution_changes.aspx
Annual rebalancing of Russell Indexes
In order to maintain true representation of global equity markets and avoid capitalization and style slippage, Russell annually rebalances the entire Russell family of indexes.
Annual reconstitution ensures that the Indexes reflect the changes in the market over time and accurately represent the true opportunity set of institutional managers. Russell's U.S. and global index families reconstitute simultaneously.
2010 Reconstitution
The 2010 reconstitution of the Russell Indexes will take place after the market closes on June 25, 2010.