My project was to study and catalogue the nearly five hundred late Roman and Byzantine weights in the collection of the Istanbul Archaeology Museum. There are mainly two groups of weights: commercial weights and coin weights. Since the photographs and the technical measurements of the weights were taken previously in the museum, I classified them according to their forms and units, and was thus able to make a tentative catalogue of them during my two-month residence. The chronological span for the weights ranges from the fourth century through the thirteenth century AD. The weights were classified in eight main types: (1) spherical commercial weights, (2) circular commercial weights, (3) square commercial weights, (4) octagonal commercial weights, (5) circular coin weights, (6) square coin weights, (7) octagonal coin weights, and (8) bowl-shaped weights. Types 2, 3, 5, and 6 form the majority in number. While type 1 consists of Late Roman weights, the other types are Byzantine weights. All the weights (except for the bowl-shaped ones) are engraved or punched on the top with the denominational mark, mainly inlaid with silver. The largest unit is a 3 libra weight weighing 975 grams; it is among the circular commercial weights (type 2). Nearly all of the weights were classified and catalogued by their forms, units, and chronology.