Anhydride polymers that release active or activatable agent(s) have pre-selected properties such as molecular weight, flexibility, hardness, adhesiveness, and other valuable properties. The polymers are suitable for use in compositions, formulations, coatings, devices, and the like that benefit from the controlled release of an agent(s) over a period of time. The polymers are prepared by a process involving various alternative and sequential steps that allow the design a priori of products with specific characteristics. The polymers are suitable as delivery systems, either by themselves, as compositions, formulations or devices.