This article describes the synthesis of biodegradable polyphosphazenes. The rate of degradation can be varied in a controllable manner by the introduction of hydrolysis-sensitive amino acid ester side groups or by blending of polymers. Biodegradable polyphosphazenes can be used for the preparation of drug-containing implants and this is illustrated for devices containing the cytostatic agent mitomycin C. This article reviews data about the degradation characteristics of poly[(amino acid ester)phosphazene] derivatives that have been discussed previously. Some new data about MMC-containing poly[(organo)phosphazene] devices are discussed as well.