This paper presents an excellent review of the many different techniques used to prepare molds and casts at the British Museum (Natural History). The use of silicone rubber (RTV), latex, polysulphide rubber, alginate and vinamold in the preparation of molds and poly(ethyl methacrylate), polyester and epoxy resins and polyurethane foam in the preparation of casts is described. Methods of keying, coloring and separating are also described.