After a brief survey of the factors that affect the permanence of photographs, and of the basic measures necessary to ensure their protection, the text breaks down the study of the properties, availability of conservation treatments for, and response to treatments of 10 groups of photographs, arranged in approximate chronological order. These include the following: paper negatives (mid-1830s to mid-1860s, rare); salted paper prints (1830s to mid-1860s, rare); wet collodion glass plate negatives (early 1850s to late 1880s); encased photographic pictures (daguerreotypes, ambrotypes, and tintypes); silver gelatin dry plate negatives (early 1880s to present) cellulose nitrate films (1890s to 1951); safety film negatives (late 1920s to present); and black-and-white paper prints with a distinct image layer (silver albumen and silver gelatin, early 1860s to present). Albums containing photographs are covered, as well as color negatives and slides. The list of conditions affecting a photographic collection that warrant the attention of a conservator concludes the text.