Stepping into the lives of men and women who until recently were slaves demands the softest of treads.
The experience of being enslaved - forced to work for no pay, often under the threat of violence and with no hope of escape, burns deep and leaves wounds which take a long time to heal.
From impoverished and often illiterate Thai farmers to women forced into prostitution; from men tricked into servitude in Brazil's brutal charcoal industry to entire families trapped as bonded labourers in Pakistan's feudal brick kilns; we met and filmed dozens of slaves for this series.
Food Chain Slaves. It is a nation built on the abolition of slavery, but there are at least 40,000 slaves in the US today. In the opening episode of Slavery: A 21st Century Evil, Al Jazeera's Rageh Omaar investigates food chain slavery in the US.
Sex slaves. There are an estimated 1.4 million sex slaves in the world today and international trafficking is on the rise.
Bonded Slaves. It is a form of slavery that is passed down from one generation to the next, enslaving millions.
Child Slaves. There are at least 8.4 million child slaves in the world today, many of them held as forced labour.
Charcoal Slaves. Poverty-stricken men from the north of Brazil are often lured to remote camps where they are used as slave labour.
Bridal Slaves. In the midst of widespread poverty, fueled by economic inequality and rampant corruption, a new form of slavery - bridal slavery - has flourished in India. Women and young girls are sold for as little as $120 to men who often abuse them.
Prison Slaves. Over the past 20 years China has become the world's biggest exporter of consumer goods. But behind this apparent success story is a dark secret - millions of men and women locked up in prisons and forced into intensive manual labour.
Bonus: Al Jazeera slavery debate. Luis C d'Baca from the US State Department Office to Monitor and Combat Trafficking in Persons; Kevin Bales, president of Free the Slaves; David Batstone, president of Not for Sale; and Joy Ezeilo, UN Special Rapporteur for Trafficking in Persons.