The Cotswolds, while not a very large region geographically (it's about the size of the Tokyo region of Japan according to the tourist board), does encompass several different towns, making driving the best way to get around and see everything.  Public bus services do exist, however, and if you prefer not to drive you can easily obtain local schedules from any hotel or shop. 

If you do decide to drive your way around the Cotswolds there are a few things to remember, especially if you are not familiar with the region.  Most importantly you must remember to drive on the LEFT side of the road.  A primer for English road signs, something you must understand before driving there, can be found at the Tourist Board's driving page.  Also be sure that you have all of the drivers license requirements needed to drive in England and that you are prepared for the much higher price of fuel there. 

Maps of the Cotswold region are available at all car rental offices and service stations.  A very good interactive map of the area is also available online at the Tourist Board's website.  Car rentals are available at the Heathrow airport as well as at several locations in the Cotswolds' towns themselves.