She was accompanied by Prince Philip as she cut the ribbon on the £1.35bn road bridge - exactly 53 years after she opened the Forth Road Bridge. The Queen said the structure, the UK's tallest bridge, was a "breathtaking sight" and one of three "magnificent structures" across the Forth.
First Minister Nicola Sturgeon said people would "marvel" at the bridge in 100 years. The Queen met children and officials at the south end of the bridge and was given a floral posy by Elizabeth Martin, grand-daughter of crossing project director Michael Martin.
After cutting the ribbon to cheers from the watching crowd, the Queen then travelled by car across the bridge.
She then made a speech and unveiled a plaque to declare the crossing formally open. There was also a fly-past by the Red Arrows and a flotilla of boats travelled under the bridge as the national anthem was played...