Search engine of Italian buses

The accepted answer concerns local buses and recommends trains for long-distance journeys. However especially for travel to the south of Italy, this is not always the most convenient option.

To the best of my knowledge there is no search engine that covers all long-distance bus lines of Italy. Typically I proceed as:

• Search on iBus
• Search with Rome2Rio
• Google for further direct bus links using "autobus/bus/pullman departure city destination city", e.g. "pullman Roma Matera". It is recommended to use Italian city names here, as not all services may be advertised in English.
• Maybe you are lucky and your departure or destination city has a bus terminal that lists departures/arrivals, this could give a good overview of existing lines. Search for "stazione pullman city".
• If you know someone from the area (especially students), you could ask them how they typically travel - I discovered some bus lines this way that I was not aware of.

Then take the best result you get from these searches and proceed to booking either via the search engines above or from the bus company directly (often slightly cheaper).

Italy is also covered by Google transit. I don't know how good it is for Italy, but for my home town it is quite good.