In this paper we introduce a new interpretation of business and IT agility -- a calculus of business change and the resultant IT change. We argue that business agility, the ability to respond with "smooth and dexterous performance" derives from a coordination structure for the business with strong implications for day to day operations. We relate the argument to an operational modeling approach that we have developed as well as with other contemporary concepts on complexity in business. Our modeling approach is distinguished by the concept of "business artifacts" and artifact-centered thinking. We have had considerable success with operational business modeling and we will draw on some examples to illustrate our arguments.