Your baby's stronger neck and arm muscles allow him to practice rolling over toward one side, a milestone that will probably awe and amuse you. Your baby might adopt rolling as his primary mode of ground transportation for a while, or he may skip it altogether and move on to sitting, lunging, and crawling. As long as your baby continues to gain new skills and shows interest in getting around and exploring his environment, don't worry.
Rolling over can be fun for your baby, but it can also be nerve-racking for you. Keep a hand on your baby during diaper changes, and never leave him unattended on a bed or any other elevated surface.