The H&M group sells an estimated three billion articles of clothing per year. Its revenue makes it among the top three fashion retailers in the world.

Clothing for its brands, including H&M, Arket and & Other Stories, is manufactured in 40 countries, the company said; in Bangladesh alone, it sources from 275 factories that employ half a million workers.

As it sprawls ever farther around the globe, hopping from trend to trend, how can H&M keep track of how the skirts, pants and sweaters it sells are made? How, for example, can it monitor whether, in faraway countries, workers are being paid less than they need to live, forced to work hours of overtime in precarious conditions?

This spring, after almost three years of preparation and coordination by 40 team members from Hong Kong to Stockholm, and at a time when scrutiny of the global fashion industry and its shadowy supply chain is greater than ever, H&M introduced an effort to do exactly that — and to make it public for shoppers.