Hornsby is a suburb in the Northern Sydney region, or Upper North Shore of Sydney in the state of New South Wales, Australia, approximately 23 kilometres (14 mi) north-west of the Sydney central business district. It is the administrative centre of the local government area of Hornsby Shire.

Hornsby is 25 kilometres (16 mi) by train and about 24 kilometres (15 mi) by road from the Sydney central business district. Hornsby railway station is the junction of the T1 North Shore and the T9 Northern Line of the Sydney Trains network and is a hub for some services and is connected via bridge to Westfield. There are frequent railway services to the central business district via Strathfield or via Gordon. Intercity and regional trains also stop at Hornsby on the way to the Central Coast, Newcastle and further north.

Bus services operate from Hornsby Station Interchange. Services are operated by CDC NSW. to local residential areas including Hornsby Heights, Westleigh, Normanhurst, Thornleigh, Wahroonga, Warrawee, Turramurra and St Ives.

Residential areas, consisting of low-to-medium density housing, are located on both sides of the railway line. Many of residential areas on the western side of the train line enjoy bushy surrounds and close proximity to Regional and National Parks, as well as the beautiful Lisgar Gardens.

In recent years, high-rise apartments have been constructed adjacent to the train line as part of the NSW state planning policies to allow medium to high density development along transport corridors.

Hornsby is home to a number of schools, including primary schools Hornsby North Public School, Hornsby South Public School, Hornsby Heights Public School and Clarke Road Special School and the secondary schools Barker College and Hornsby Girls' High School, which is a selective school. There is also a TAFE College at the north-western side of Hornsby.