For heavy public transport use in Hong Kong, buy an Octopus Card, a rechargeable ticket for travel on the MTR and KCR lines, the Airport Express (AEL), Light Rail, trams, most buses, most ferries and minibuses. The card costs an initial HK$150, comprising HK$100 useable value and HK$50 deposit (there’s no refund if you return the card within three months, however). When it runs out you add credit at machines in rail stations or over the counter at any 7-Eleven store. The cards are available from MTR, AEL and KCR ticket offices.

To use, scan them over sensors at the ticket gates.

Octopus also offers a Tourist Pass (HK$50), valid for 24 hours from the first time that you use it and allowing unlimited travel on the MTR (but not the AEL); and an Airport Express Tourist Card (HK$200/300 including a HK$50 refundable deposit) for use on the AEL (either single or return according to price) and 72 hours unlimited travel on the MTR after the first time you use it.