A discussion is presented of the two primary ways of understanding software costs. The black-box or influence-function approach provides useful experimental and observational insights on the relative software productivity and quality leverage of various management, technical, environmental, and personnel options. The glass-box or cost distribution approach helps identify strategies for integrated software productivity and quality improvement programs using such structures as the value chain and the software productivity opportunity tree. The individual strategies for improving software productivity are identified. Issues related to software costs and controlling them are examined and discussed. It is pointed out that a good framework of techniques exists for controlling software budgets, schedules, and work completed, but that a great deal of further progress is needed to provide an overall set of planning and control techniques covering software product qualities and end-user system objectives.>