A boy rides a bike towards a brick kiln outside of Varanasi. India is home to some 18.3 million modern slaves, 40 percent of the global total, according to the Walk Free Foundation. Hundreds of thousands of them work in brick kilns in Uttar Pradesh, India’s most populous state, in dangerous and squalid conditions. Slavery – which includes child marriage and bonded labor – remains a big challenge and a source of shame in India amid the nation’s recent rapid economic growth. The sheer scale of the problem makes it very difficult for the government to tackle it alone. Nongovernmental groups try to ensure that what little aid is available, such as food and housing, reaches those who need it most.