Many groups and individuals have challenged Scientology's legitimacy as a religion.
Scientologists have faced opposition from the medical community over the religion's claims about mental health, from the scientific community over its claims about its E-meters and from other religious groups about its status as a religion.
"It's part therapy, part religion, part UFO group," says Bromley. "It's a mix of things that's unlike any other religious group out there."
For a long time, the Internal Revenue Service denied the Scientologists' attempts to be declared a church with tax-exempt status. But the IRS granted them that status in 1993.
Many members say the church is largely about self-improvement. "What I believe in my own life is that it's a search for how I can do things better, whether it's being a better man or a better father or finding ways for myself to improve," Tom Cruise recently told Playboy magazine. "Individuals have to decide what is true and real for them."