Queen Elizabeth II has signed a charter calling for an end to discrimination across the Commonwealth to keep the group of nations "fit and agile".
She made a brief speech before signing the document, which significantly aims to improve gay rights.
"Throughout the ages charters have been seen as special documents, designed with care to stand the test of time," she said.
"The charter I will sign today on behalf of you all represents a significant milestone as the Commonwealth continues its journey of development and renewal."
The 86-year-old monarch was at pains to not specifically mention gay rights.
But she says the charter will "light the path" for all 54 Commonwealth countries to follow.
"I hope the carefully chosen words of the charter will re-invigorate efforts already begun to make the Commonwealth fit and agile for the years ahead, so that it can apply its global wisdom in the hopes and needs of this and future generations," she said.
The Queen has been recovering from a stomach bug which put her in hospital last week and forced her to cancel appearances at some Commonwealth Day events taking place in London.
The 16-point charter was adopted in December by all Commonwealth nations.
It aims to protect democracy, the rule of law, international security and free speech.