Newton was one of two people credited with the creation of calculus, but even though he developed his ideas first, he did not get them printed first. A German mathematician, by the name of Leibniz, released his findings almost 9 years before Newton did. Both men approached the concept of calculus differently and held different views, so often both men are credited with its creation.
These two men created or discovered calculus, but it was French scientists that perfected the method that the two men had put together. The different methods put forward by the two men were blended together to create what is used today after many years of clarification by other mathematicians.