Simple example: I create a Person class that has one instance variable named 'name'. I've created a few instances and put them in a collection "Person allPeople". Now I change Person's definition to have the instance variables 'firstName' and 'lastName' and remove the instance variable 'name'. The Person instances I have now have instance variables 'firstName' and 'lastName' set to nil. When I'm developing locally it is okay (if irritating) for me to wipe out any objects that I have in memory and start again. More importantly, I don't have the first clue how I'm going to deploy code and keep it up to date. I can get the new code in via Monticello, but what good is that if it wipes out all of my data? I feel stupid asking because I'm sure there's some aspect I'm missing, but please help me out here because I'm not seeing it. Pat