In 2005 the Peruvian government made many changes to the management of the Inca Trail to protect its fragile eco-structure from over-use.
Most of these changes were aimed at reducing the number of trekkers on the trail, improving the quality of the tour operators and managing a reservation system forcing hikers to make their reservations at least 4 months in advance.
The number of hikers (including porters and guides) allowed on the Inka Trail is strictly regulated and limited to 500 per day.
Permits are issued for each individual trekker by full name, nationality, passport number, birthday, age and must be obtained 5-4 months before the day trek commences, a nightmare for casual arrivals/gap year travellers etc! But unsurprisingly if you show up in Cusco with a few spare dollars in one hand someone may well find you a permit!
Alternative? See Choquequirao.
According the new regulations it is mandatory to join a group through a tour operator and they will organize the trekking date. The tour operator is responsible for organizing a guide, cooks, registered porters, entrance fees, camping equipment and the campsite.