Viby, often referred to as Viby Sjælland (usually styled Viby Sj) to distinguish it from Viby J in Jutland, is a satellite and commuter town to Roskilde and Copenhagen, located 8 km south of Roskilde, in Roskilde Municipality, some 30 km west of Copenhagen, Denmark. The original village, now Gammel Viby ("Old Viby"), is located in the northern part of town while the modern district has formed around which opened on the Danish Main Line between Copenhagen and western Denmark in 1854. The village of Dåstrup is now also an integrated part of Viby. As of 1 January 2022, Viby had a population of 4,773.