Jeanette, this is likely to be a foundation shifting, but can you give us a little more detail here?
Is this occurring in just one or two areas? How large are the cracks, inside and out? Near outside corners? Over a slab, basement, crawlspace, or combination of these? Poured concrete basement/foundation walls, or block/stone? If basement, can you see cracks in basement walls? Any water problems (drainage outside and/or water in basement/crawl)? Do you know if you live in an area where there is a lot of clay in the soil? How old is the home, and when did this first occur?
Depending on what's happening, you may not be able to sell the home without first doing repairs, so don't jump the gun in the idea that selling will be the right answer.
Post back with some further information which will help determine the nature and extent of the problem.