Pasteurization is a process that kills harmful bacteria by heating milk to a specific temperature for a set period of time. Pasteurization kills harmful organisms responsible for such diseases as typhoid fever, tuberculosis, diphtheria, and brucellosis.
Research shows no meaningful difference in the nutritional values of pasteurized and unpasteurized milk. Pasteurized milk contains low levels of the type of nonpathogenic bacteria that can cause food spoilage. Pasteurization basically separates bacteria and germs from the raw milk.
Homogenization is an entirely separate process that occurs after pasteurization in most cases. The purpose of homogenization is to break down fat molecules in milk so that they resist separation. Without homogenization, fat molecules in milk will rise to the top and form a layer of cream.