Hi Jeff, As far as I know, they all use the same speech engine, but there are differences in other features such as support for programming etc. There is a comparison table on the Nuance website at: - http://www.nuance.com/ucmprod/groups/dragon/@web-enus/documents/collateral/n c_025214.pdf Hope this helps, if you have any queries, please let me know. Best wishes, Brian.