The Walk Free Foundation describes modern slavery as "situations of exploitation that a person cannot refuse or leave because of threats, violence, coercion, abuse of power or deception."
Common forms of slavery include forced labor, sex trafficking, bonded labor and involuntary domestic servitude.
The group says some form of modern enslavement is prevalent in 167 countries today. What's more, the number of enslaved victims has risen by 28 percent since the last index was published in 2014.
But experts say that jump is likely the result of better data collection and research methodology.
The report also applauds several countries working to combat modern slavery. The organization gives a thumbs up to the Netherlands, the U.S., the U.K., Sweden and Australia among others for their efforts to end the practice.