The Zillertal is the biggest valley branching off the Inn valley in Tyrol, Austria drained by the river Ziller. It is surrounded by the strongly glaciated Zillertal Alps to the south and east, the lower grass peaks of the Kitzbühel Alps to the east and Tux Alps to the west. The largest settlement is Mayrhofen.
The Zillertal branches from the Inn trench near Jenbach, about 40 km northeast of Innsbruck, running mostly in a north-south direction. The Zillertal proper stretches from the village of Strass to Mayrhofen, where it separates into four smaller valleys, the Tux valley and the sparsely settled, so-called Gründe - Zamsergrund, Zillergrund and Stilluppgrund. Along the way, two more Gründe and the Gerlos valley, which leads to the Gerlos Pass and into Salzburg, branch off.
Unlike other side valleys of the Inntal, the Zillertal rises constantly, but only marginally, from one end to the other - only about 100 m over 30 km. Permanent settlements cover about 9% of the entire area of the Zillertal municipalities.
Tourism has become the dominant economical factor in the valley in the second half of the 20th century and beyond. There are now (as of 2003) 6 million nights spent by tourists in the valley, mostly during winter sports holidays. Following a phase of mergers by building connecting lifts during the 1990s and early 2000s, there are now four big ski areas and three smaller satellite areas in the valley, with a combined total of more than 170 lifts and more than 630 km of downhill slopes.