Hello John, The only difference is that you shouldn't use 'would' for past states but you can use 'used to'. http://learnenglish.britishcouncil.org/en/quick-grammar/past-habit-used-towouldpast-simple Hope this helps Bob

You can use 'would,' to describe events that occurred in the past provided they occurred more than once. You can also use "would," to describe conditional events that have the sense of being in the past. "When I was young, I used to walk to school." "When I was young, I would walk to school." The meaning of these two sentences is identical, John. The only difference between the terms, then, is that you cannot use the construction "used to," in any tense other than the past tense because the verb "to use," is in the simple perfect tense in that construction. So you can use 'would,' in a conditional sentence even if the sense of the sentence is not in the past , but not 'used to.' "If I could find a way to earn more money, I would buy a new car." but also (using would in the sense of a conditional sentence that applies to something from the past): "If I had had more money, I would have bought the Ferrari instead of the Skoda."

Would is also used in past form e.g. I would meet him, I used to meet him - same meaning I used to go to school. I would go to school. - same meaning I would often go for swimming after school. I used to go for swimming after school - same meaning

I think they are mostly interchangeable. But 'I used to' is used more when the thing that was done then, is not done anymore. The difference however is extremely subtle, so maybe I am imagining things.