It’s the Day of the Girl today.
Started in 2011 by Plan International and the United Nations. The day is also known as International Day of the Girl and International Day of the Girl Child.  
This day highlights the importance of girls in the world. Girls’ health, education, and access to rights, and ability to advocate for rights denied in developing countries has a complex and long-term effect on the quality of life in countries striving to develop. When girls’ overall social and physical well-being are ignored, when child marriages are common, developing communities have higher rates of domestic violence, maternal mortality, infant mortality, child undernourishment, and lower rates of primary school participation and completion.  
Each year, The Day of the Girl has a theme to focus global development efforts. In the past, themes have revolved around ending child marriage, and the importance of education. This year the theme is “Girls’ Progress = Goals’ Progress: A Global Girl Data Movement”. Data gathering is the theme this year because meaningful data on the challenges of women and girls in the world is vital for the 2030 Agenda for Sustainable Development.  
Improving the lot of girls in a community has the potential to break the cycle of poverty. Education is a key tool in forcing the betterment of girls. Child marriage (under 18, often under 15) is a common problem in developing areas, partially due to cultural and financial pressures. Child marriage increase the risk for domestic abuse, material mortality, and offspring who don’t become vaccinated or encouraged to complete primary education. Girls who complete primary education and participate in secondary education are significantly less likely to marry under age against their will, and are far more likely to provide adequate nutrition and healthcare to their children, as well as encourage them to complete primary education.   
Thousands of events are held around the world to commemorate women’s achievements and celebrate girls’ potential. These events take on local flavor and significance. Among many others, they include a live stream with First Lady Michelle Obama and Glamour Magazine to promote #letgirlslearn and a UN sponsored concert in India.   
Here's some key data on girls around the world.