The Queen has opened the centenary annual meeting of the Women's Institute (WI) at the Royal Albert Hall in London.
Praising the WI for continuing to grow and evolve with its members, the Queen said so much had changed for women in British society.
But the WI has been a "constant throughout", she said.
The monarch, who became a member of Sandringham WI in 1943, congratulated members on the "significant occasion".
In a speech to more than 5,000 attending WI members, the Queen said: "There has been significant economic and social change since 1915. Women have been granted the vote, British women have climbed Everest for the first time and the country has elected its first female prime minister."
Throughout this change, she said the WI had gathered women together, encouraging them to acquire new skills and nurturing unique talents.
She added: "In the modern world, the opportunities for women to give something of value to society are greater than ever, because, through their own efforts, they now play a much greater part in all areas of public life."
Over the past 100 years, the WI has continued to stay "relevant and forward-thinking", she said.
The Queen added: "In 2015 it continues to demonstrate that it can make a real difference to the lives of women of all ages and cultural backgrounds, in a spirit of friendship, cooperation and support."
Duchess may join
The Queen attended the event with the Princess Royal and Countess of Wessex - all three are members of their local branches or federations.
Janice Langley, the WI's chairwoman, revealed hopes that the Duchess of Cambridge may join her local branch, the Amner WI. She said the branch had written to the Duchess, who apparently expressed some interest in the organisation.
Mrs Langley added: "It would be wonderful if she carried on a long tradition of members of the royal family enjoying WI membership and everything that's on offer through the WI - and hopefully Princess Charlotte will follow in due course."
The Queen, who over the years has attended meetings near her Sandringham estate in Norfolk, presented the Lady Denman Cup to the winner of the WI's creative writing competition.
Before leaving, the Queen shared a joke with the Princess Royal and the Countess of Wessex as she tried to cut a very thick and rich fruit cake baked to mark the centenary of the WI.
Julie Clarke, 67, chairwoman of the WI's North Yorkshire West Federation said: "It was a rich fruit cake and she was guaranteeing it was definitely a fruit cake by trying to cut to the bottom. The rich fruit cake needs some cutting and she just got a bit of assistance from Anne to get the knife through."
The Queen also received the WI's commemorative baton, which has been travelling to some of the WI's 6,600 branches across 69 federations in England, Wales, Jersey, Guernsey and the Isle of Man.
The centenary baton was designed to celebrate the friendship and community between the organisation's 212,000 members.
Footage of its journey around the UK was shown at the Royal Albert Hall and the event linked live to members in Anglesey, where the first Women's Institute was formed.
At the scene: Sangita Myska, BBC news reporter
The Queen walked on stage here at the Royal Albert Hall to rousing applause and cheers from members of the WI.
Her Majesty was clearly touched by the greeting: looking around the hall, she smiled and waved at the thousands of delegates.
The ceremony has both formal and personal significance for the Queen, for it was in 1943 that she joined the Women's institute in Sandringham, becoming president and attending annual meetings.
It was also in the 1940s that the WI earned its reputation for jam making - turning some 5,300 tonnes of fruit into preserve, to help with food shortages during World War Two. The first WI was founded over two decades earlier in Anglesey.
A formidable, practical force, it brought education to poor women living in rural areas. Though a non-political organisation, it backed revolutionary campaigns including voting rights for women, demands for equal pay and better information about sexual health.
The WI currently has around 212,000 members countrywide - a membership some political parties would envy. But the organisation is not resting on its laurels and is aware that to remain relevant it will have to attract a diverse and younger membership.
Inspired by an idea from Canada, the first WI was founded in the village of Llanfairpwllgwyngyll - famous for having Britain's longest place name - on 16 September 1915.
The WI was set up during World War One to rejuvenate rural communities and encourage women to become more involved in food production amid German naval blockades.
But today the WI says its aims have broadened and it is now the largest voluntary women's organisation in the UK.
On Tuesday, the Countess of Wessex and the Duchess of Cornwall hosted a garden party at Buckingham Palace to celebrate the centenary.
They met some of the WI's most famous members - the Calendar Girls - whose semi-nude appearance in a fundraising calendar in 1999 was immortalised in the hit movie starring Helen Mirren and Julie Walters. To date they have raised more than £3m for research into leukaemia and lymphoma.
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