Italy is a country of enormous diversity and contrast. Most famous are the Alps. Coming from the efficient neatness of Switzerland or Austria, the Italian Alps are wilder and at the same time more tranquil, like stepping back in time. The most beautiful and popular areas are Gran Paradiso, Val Grande, Stelvio and the Dolomites.
In addition there are countless national parks, all very much worth hiking through. A series of mountain ranges runs from north to south like a backbone, starting from the hills of Tuscany, to the Apennines and Abruzzo to Italy's toe, Calabria. Southern Italy, too far for many tourists, has several attractive hiking regions, like Pollino and Aspromonte.
In the Alps you can walk from hut to hut, elsewhere you can do day hikes, such is the rule in general. However some genuine long distance hiking trails are under construction. European long distance trail E10 in the Alps, which coincides with the 1000km long Grande Alpine Trail and the international Via Alpina. The second large project is the E1, which coincides with the Grand Apennine Mountains Trail and the Ligurian Mountains High Trail. If this trail is ever completed, you can start from Como passing Genova and continue all the way to Reggio di Calabria and Palermo or Siracuse on Sicily. The third large project means to join all these trails into one 6000km long Sentiero Italia. Last but not least, there is the Alta Via in the Dolomites: splendid walking.
Mountain huts abound in the Alps. Hiking can be done all summer, from June until well into October. Further south spring is the best hiking season. In April you will still get stuck in the snow up in the mountains. Autumn is supposed to be fine as well, but alas, as one hiker put it: "you wake up to the sounds of church bells and gunfire". As hunters, Italians are best avoided.