Most foundations will experience some degree of cracking during its life. Some concrete cracks occur as the result of the curing process or are common shrinkage cracks. Other foundation cracks can occur for various reasons:
Frost
Shrinkage or swelling of the clay supporting the foundation under the footing.
Changing the loading on the structure (e.g. Adding a second story to a single story dwelling).
If these cracks leak water or if they appear to widen as time passes, it can be an indication of a developing problem.