The Inca Trail, was used by the Incas to get to Machu Picchu and is also the most famous trail today for tourists trying to get there on foot, is considered sacred and during the trail you can see many archaeological sites like Llaqtapata, Runkuraqhay and Wiñayhuayna before arriving to the sacred city of Machu Picchu.
Every February the trail is closed for hikers, because the route needs to be cleaned. In 2004, the Peruvian government passed a law concerning the Inca Trail to Machu Picchu.
The regulations restrict the number of people permitted to enter the Inca Trail to 500 per day. Of the 500 people allowed daily on the Inca Trail, only about 150 are trekkers, since the rest of the spots are reserved for the guides, cooks, and porters. The trekking companies who are allowed to work the Inca Trail have to have an operating license specifically for the Inca Trail (operating licenses are issued yearly) and those trekking companies also need to have an office in Peru.
The most popular Inca Trail trek is the Classic Inca Trail and those spaces are reserved quickly! It's advisable to book your Classic Inka Trail trek months to a year in advance and only afterwards book the rest of your trip to Peru (flights, other tours, hotels, etc.).
The tickets sold according to the new regulations are nonrefundable and nontransferable, but there is no limit of how long beforehand you can buy them. During the peak season (between June and October), the spaces sometimes fill up six months in advance!