The National Geographic Society has a very large and valuable collection of color photographs, including about 10,000 Autochrome plates and films acquired between 1909 and 1938. Until recently these old photographs were stored under quite varied conditions and their state of preservation ranges from excellent to very poor. A restoration program was initiated two years ago, but lack of information about the intrinsic stability of Autochromes and their aging behavior led to the commissioning of a pilot project in 1981 aimed at developing the data required for specifying optimum storage conditions, and for devising the best methods of ensuring ready access to the collection while safeguarding the valuable originals. In the course of this project over 11,000 additive type color plates and films were examined and detailed data collected on their physical condition and photographic quality as well as on the type, frequency, and severity of defects and aging blemishes. The probable causes of these defects have been determined and accelerated aging tests carried out to assess the dark and light stability of Autochrome images. Copies were made also of a representative assortment of good and poor originals with five color films at four reproduction scales to establish the most useful method and formats for producing high-quality copies that will be needed for safekeeping, for study, for dissemination, and for further photographic and photomechanical reproduction. The information gained during this investigation will be reviewed and conclusions drawn regarding suitable methods and procedures for preserving Autochrome plates and films.