In more than two decades in the charity sector, I've been involved in a lot of campaigns about a lot of different issues. I've spent my professional life fighting for the rights of the most vulnerable children in the world and in that time we've take many strides forward in improving healthcare, sanitation and education systems.
But it's rare that I've felt so optimistic about the potential for change as I do about the chance we have in the coming months and years to get it right for the world's girls.
Let's be clear about the scale of the problem. For me there is no greater injustice in the world than the mass violation of the rights of millions of girls around the world - violations that happen just because of their gender.
The statistics are utterly shameful. Every two seconds another girl is forced or coerced into marriage. Every ten seconds a girl is at risk of female genital mutilation. Every seven minutes a girl dies in childbirth because her young body just isn't ready. And every day 65 million girls don't go to school, denied the opportunity simply because they are girls.
But behind these statistics, of course, lie the real lives of girls around the world. Take Christiana, from Sierra Leone. She was top of the class when she first started school. But when her parents could no longer afford the fees, her potential was thwarted.
Forced into a marriage she did not choose with a man old enough to be her grandfather and subjected to FGM in order to be approved by her husband, Christiana was sexually and physically abused.
Christiana's story is a shocking example of how the unique challenges faced by adolescent girls can compound one another.
Plan worked with Christiana to help turn her life around. Now she is the leader of her local Girl Power group, supporting other girls to overcome the challenges they face and encouraging them to stay in school. Last month, she attended a youth takeover of the African Union in Addis Ababa to lobby world leaders to fund education.
It's the courage of girls like Christiana, prepared to tell their stories so that the same story can't be told for their daughters, that means that the abuses faced by girls are now top of the agenda and cannot be ignored. Christiana is joined by Fahma Mohamed and Muna Hassan, who successfully campaigned for schools to receive more information about FGM; by Malala Yousafzai, who took her fight for education to the highest possible level; and by countless other girls around the world who may not attract the headlines but who together are crying out for the abuse of girls to end.
Thanks to these girls we now face an opportunity that we simply cannot fail to grasp. And I'm full of confidence that we will grasp it.
The signs are positive. Last week at the Global Partnership for Education replenishment conference in Brussels, donors and governments pledged £16 billion to fund education over the next four years. And with girls disproportionately affected by the chronic underfunding of schooling to date, it's girls who will benefit most.
Last year, DfID launched a £35million fund to end FGM in a generation, a battle in which we must wholeheartedly support them. And in just a few weeks, the Girl Summit, led by David Cameron, will bring to the political agenda both FGM and child marriage like never before.
But most of all, people in the UK - and indeed around the world - has woken up to the reality that millions of girls are left out and left behind simply because they are girls. The reaction to Malala's cause, the global outcry at the abduction of hundreds of school girls in Nigeria, the support for Fahma - we are simply no longer content to let these issues pass us by, and decision-makers can't fail to have noticed.
So as we re-launch the world's biggest campaign for girls' rights this week - Because I am a Girl - we do so in the belief that, with people holding feet to the fire across the planet, real progress can be made. It's time to get it right for girls.