Planned Parenthood has been a polarizing organization since its precursor, a clinic in Brooklyn, New York, was founded in 1916 by pioneering birth-control advocate Margaret Sanger. It provides a range of health services - including cancer screenings, testing for HIV and contraception - but its role as the No. 1 abortion provider in the United States has for many years made it the focus of violence, boycotts, protests and attempted sting operations by anti-abortion activists.