From modest farmhouses to great buildings plaster has traditionally been used to finish interior walls. A versatile material, plaster could be applied over brick, stone, half-timber, or frame construction. It provided a durable surface that was easy to clean and that could be applied to flat or curved walls and ceilings. Historic plaster may first appear so fraught with problems that its total removal seems the only alternative. But there are practical and historical reasons for saving it. First, three-coat plaster is unmatched in strength and durability. Next, replacing plaster is expensive. Of more concern to preservationists, however, original lime and gypsum plaster is part of the building's historic fabric. Plaster can also serve as a plain surface for irreplaceable decorative finishes. For all of these reasons, plaster walls contribute to the historic character of the interior and should be left in place and repaired if at all possible. Plastering is a skilled craft, requiring years of training and special tools. While minor repairs can be undertaken by building owners, most repairs will require the assistance of a plasterer. The approaches described here stress repairs using wet plaster, and traditional materials and techniques that will best assist the preservation of historic plaster walls and ceilingsmand their appearance. Dry wall repairs are not included here, but have been written about extensively in other contexts. Finally, a replacement option is described for use when historic plaster cannot be repaired. Thus, a veneer plaster system is discussed rather than dry wall. Veneer systems include a coat or coats of wet plastermalthough thinly appliedmwhich can, to a greater extent, simulate traditional hand-troweled or textured finish coats. This system is generally better suited to historic preservation projects than dry wall.