Almost one-third of American workers now do some kind of freelance work—and they lack almost every kind of economic security that permanent full-time workers have traditionally had.

Though exact figures are impossible to find, many experts and labor organizers estimate that about 30 percent of U.S. workers are “contingent.” That means they don’t have a permanent job. They work as freelancers, temporary workers, on contract, or on call, or their employers define them (often illegally) as “independent contractors.”

Their ranks include writers and warehouse workers, janitors and business consultants, truck drivers and graphic designers—and their number is rising. Richard Greenwald, a sociologist of work and professor at St. Joseph’s College in Brooklyn, estimates that their share of the U.S. workforce has increased by close to half in the last ten years. In July, Staffing Industry Analysts reported that the average share of contingent workers at companies it surveyed had gone up by one-third since 2009, to 16 percent. Last year, a different survey found that contingent workers averaged 22 percent of the workers at 200 large companies.