Change Tracking in SQL Server 2008

SQL Server 2008 introduces a new feature implemented through the CHANGE_TRACKING database option. Change tracking is a lightweight mechanism that associates a version with each row in a table that has been enabled for change tracking. Each time the row is changed, the version number is incremented. Instead of building systems to avoid changes from multiple users overriding each other, applications need only compare the row version to determine if a change has occurred to the row between when the row was read and written.

After change tracking has been enabled for the database, you can choose which tables within a database that change tracking information should be captured for. Over time, change tracking information accumulates in the database, so you can also specify how long tracking information is retained through the CHANGE_RETENTION option and whether tracking information should be automatically cleaned up with the AUTO_CLEANUP option.

A nice explanation on this topic can be found on this screencast by Mike Taulty.

For an exhaustive explanation on this topic, check it out on BOL.