William Bell was an active photographer for more than a half century, successfully making the technical and commercial transitions from the daguerreotype process of the 1840s and 1850s to the collodion processes of the 1860s, 1870s, and 1880s, and finally to the dry plate processes that dominated the medium from the mid-1880s until the time of Bell's death in 1910. The purpose of this thesis is to provide a biography of Bell (1830-1910), to assess his contributions to photography, and to suggest something of the growth of professionalism in nineteenth century photography using Bell as "typical."