From Bolzano you can reach the most important valleys and villages by train, all other places by bus.
The capital of South Tyrol - Bolzano - is situated at one of the main European railway routes. So it can be reached easily from Munich (Germany) and Innsbruck (Austria) in the north as well as from Verona, Rome, Venice and Milan in the south. More information to the local public transport in South Tyrol you find here.
Furthermore there operates the Südtirol Transfer bus service.
from Munich EuroCity trains start approx. every two hours during the day directly to South Tyrol (via Innsbruck - Passo del Brennero - Bressanone - Bolzano). Further information: German Railway DB and Austrian Federal Railways ÖBB.
from Vienna you can go via Villach to Lienz in East Tyrol, and from there by regional trains further to the Val Pusteria in South Tyrol. Further information: Austrian Federal Railways ÖBB.
in Switzerland you can take the Rhaetian Railway to Zernez in the Engadine, and from there by bus crossing the Ofen Pass to Malles where the Val Venosta Train starts. Further information: Swiss Railway SBB and PostBus Val Venosta - Switzerland.