This thesis examines the interior glass mosaics of the Harris C. Fahnestock mausoleum within The Woodlawn Cemetery in the Bronx, New York. A conservation plan was developed to preserve the only complete mosaic interior by Louis Comfort Tiffany at The Woodlawn Cemetery. This particular design is one of Tiffany’s earliest ecclesiastical commissions and contains a rare example of a domed mosaic interior. A comprehensive evaluation of exterior envelope defined the interior mosaic deterioration. Material analysis was performed on sections of the mosaic composition. Recommendations are made for a conservation plan to prevent further deterioration of this significant mortuary decorative art.