Sofia has an extensive network of public transport, which is gradually being modernised. Bus, trolley bus and tram tickets can be bought from the machine just behind the driver's cabin. The ticket is only valid for the journey on that particular tram/bus. Many trams and trolley buses now have ticket machines at the front, where you can buy a ticket that does not need punching. Daily, weekly and monthly travel cards can be bought from kiosks or from a machine inside the bus.You can also use your debit card to pay for the trip. 
For timetable and route planner as well as changes to usual routes you can use the website.
As in most other cities; take extra precautions against pickpockets when travelling on crowded public transport.