Broken Strings James Morrison & Nelly Furtado Download 'Broken Strings' on iTunes
A big day for Olympics organisers.
The biggest test event so far begins later. It's designed to see how the Olympic Park copes as well as the armed forces.
140,000 people will watch events like athletics, wheelchair tennis and hockey.
Meanwhile the Royal Navy and RAF are testing how things will work for them in the event of a major incident.