CityBus is one of the three major bus operators in Hong Kong, it provides both franchised and non-franchised bus services. The franchised route network serves mainly Hong Kong Island, cross-harbour routes (between Hong Kong Island and Kowloon/New Territories), Ocean Park, North Lantau (Tung Chung and Hong Kong Disneyland) and Hong Kong International Airport. The non-franchised routes serve mainly City One Shatin.

2101 is one of eleven Alexander ALX500 bodied Dennis Tridents which joined the Citybus fleet in 1998. They were built as airport coaches, and have been used on the E-series external routes which links Tung Chung New Town and the urban districts, before Chek Lap Kok Airport was opened in July 1998. These 11 coaches were originally painted in Citybus corporate livery, but 2101 and 2102 were re-painted into Cityflyer livery after they joined their Duple Metsec bodied sister vehicles serving on the A-series airport routes.