Peru can be visited all year round.
The best time to visit Machu Picchu, Cusco and the Andean Highlands is from May to October, when the days are sunny and less misty but with chilly nights. July and August are the busiest months. December to March is the rainy season and the Inca Trail is closed in February. Outside of these months it can be rainy, but this offers the advantage of fewer visitors, greener scenery and abundant flora, including the orchids at Machu Picchu.
The Amazon rainforests are wet and humid all year round. If taking a river cruise, the hot high water season is from December to May and the hotter low water season is from June to November.
'Inti Raymi' - the Festival of the Sun - is the most important festival in Peru and is celebrated in the streets of Cusco in June.