The biggest event is the Gay Canal Pride Parade that will go through the Prinsengracht canal (starting 2pm at the West end of Prinsengracht). The boats will follow the Prinsengracht, then the river Amstel, Zwanenburgwal, Oudeschans, and end in the Oosterdok.
(See map of the Canal Parade route).
This event will draw some 300,000 people.

Another large event is the Amsterdam Tournament, a soccer tournament hosted by Ajax Amsterdam, of 4 international soccer clubs. Some 150,000 visitors are expected.

There are also some danceparties (at the Sloterplas lake in Amsterdam West, and the Twiske recreation area in Amsterdam North), plus the Parade will start - a yearly carnival that travels through the Netherlands and will start tomorrow in Amsterdam.

Added to the normally busy weekends in the centre of Amsterdam, this will mean a crowded town. All hotels are booked, only the very expensive ones still have some rooms left.