How long in advance do I have to book?

It all depends on the time of year. Keep in mind that the high season is from May to October (dry months) and the low season is from November to April (rainy months).

If you want to go to Machu Picchu, for example, in July and August, the most popular months, you will have to buy your tickets at least two months in advance.

If you go in the less touristy months, such as February or March, you can even buy from one day to the next.