Luhnow was the Cardinals Director of Scouting in 2005, when the club picked Greene in the first round.
A 6'2 190 utility infielder, he played primarily at 2B for the Cardinals, but the Astros will likely move him around the field to find him at bats next to All-Star 2B Jose Altuve.
The 28-year old Greene has been a bench player for St. Louis since the 2009 season. He's gotten the most playing time of his career in 2012 despite career-low batting totals, which is why the Cardinals were so eager to get rid of him while in the midst of a pennant race.
Greene is hitting .218/.272/.358 in 197 plate appearances this season, so Astros fans shouldn't expect too much from him over the next two months.
To make room for Greene, Houston designated Brian Bixler for assignment.