Lauren Said-Moorhouse, Ines Torre and Matthew Ponsford, for CNN.The wife of Microsoft co-founder Bill Gates, Today is International Day of the Girl -- a date on the annual calendar set aside to advocate for girls' rights and raise issues of gender bias. CNN spoke to some of the world's most remarkable and impressive women -- from across the fields of politics, science, media, sports and culture -- to find out: "Looking back, what one piece of advice would you give to your 15-year-old self?" Byand, for CNN.The wife of Microsoft co-founder Bill Gates, Melinda Gates is is a prominent American businesswoman and philanthropist as well as the co-chair of the Bill and Melinda Gates Foundation Getty Images

Oprah Winfrey has been a powerful force for change for young women around the world because of her own traumatic childhood experiences. In 2007 she established the Oprah Winfrey Leadership Academy for Girls in South Africa. Here is an extract from an open letter she wrote to her 15-year-old self in the May 2012 issue of O, The Oprah Magazine. Getty Images

With an outstanding career spanning three decades, Christiane Amanpour got her start in journalism as an entry-level assistant on CNN's international assignment desk in Atlanta. Working her way up to correspondent, Amanpour has since reported from every major world news event and hotspot. Today Amanpour is CNN's chief international correspondent and anchor of Amanpour, a nightly foreign affairs program Getty Images

Queen Rania of Jordan is the Queen Consort of Jordan and wife of King Abdullah II of Jordan. She has undertaken a variety of causes especially concentrating on the issue of education. In August 2009, Queen Rania was appointed the Honorary Global Chair of the United Nations Girls' Education Initiative (UNGEI) Royal Hashemite Court

Fabiola Gianotti is a world-renowned physicist at CERN and part of the team that runs the Large Hadron Collider. On July 4, 2012, Gianotti announced that a CERN team had discovered a particle consistent with the Higgs Boson -- an until now-theoretical subatomic particle long thought to be a fundamental building block of the universe. Inset: Gianotti aged 12. Mike Struik/Inset: Courtesy Fabiola Gianotti

In 2009, U.S. Secretary of State Hillary Clinton created a new role in the State Department -- Ambassador-at-Large for Global Women's Issues. Clinton's former Chief of Staff to the First Lady, Melanne Verveer was appointed to the role. Additionally Verveer had previously co-founded Vital Voices Global Partnership , an international non-governmental organization supporting global women's leadership. Today, Ambassador Verveer leads the Office on Global Women's Issues. Getty Images

Cherie Blair is a British barrister specializing in public law, human rights, employment and European Community law, arbitration and mediation. She is also the founder of the Cherie Blair Foundation for Women and is married to former British Prime Minister, Tony Blair. Inset: Blair, aged 14, as a girl guide. Getty Images/Inset: Courtesy Cherie Blair

The Belarusian professional athlete Victoria Azerenka started her tennis career from 14 years old. Two years later, she had won two junior grand slam tournaments. Azerenka is currently seeded the Women's Tennis World No.1 Player. This week she won her fifth title of the year beating Maria Sharapova at the China Open. Getty Images

Maria Shriver is an American journalist, author and activist. She describes her mission as "to inform, inspire and ignite people to impact their world as architects of change." Getty Images/Inset: Courtesy Brian Hamill

Iraqi-born Zaha Hadid is a celebrated architect and the first woman to win architecture's Pritzker Prize. Recently, Hadid designed the London Olympics Aquatics Centre AFP/Getty Images

Robin Bernstein is a historian and published author at Harvard University specializing in African and African American studies and gender studies. Kristyn Ulanday/Harvard Staff Photographer/Inset: Courtesy Brian Rafferty

Ranked the women's number two tennis player, Russian-born Maria Sharapova has had an illustrious career to date. She has won 27 women's singles titles and won a silver medal in the London 2012 Olympic Games. Getty Images

Vanessa Mae is an internationally-renowned musician who erupted onto the world stage at a young age. By 15 years old (pictured inset), Mae had released her first single "Toccata & Fugue." Getty Images