One of the first things you hear in “On the Basis of Sex” is the song “Ten Thousand Men of Harvard.” And that is more or less what you see onscreen: a parade of mostly pale males in dark suits marching through Cambridge. In their midst is Ruth Bader Ginsburg (Felicity Jones), a first-year law student and one of only nine women (out of nearly 500 students) in her class.

At a dinner party, she and the others are asked by Erwin Griswold, the dean of the law school (Sam Waterston), why they think they have the right to be there instead of the men who might have been admitted instead. The answers range from fumbling to diplomatic, but the intent of the question could not be clearer. Harvard, like nearly every other institution where power is concentrated and influence is transmitted, is no place for a woman.

That was in 1956. Ginsburg is now one of three women on the nine-member Supreme Court, and not even her most dogged ideological enemies would question her right to be there. (The Senate vote for her confirmation in 1993 was 96-3). “On the Basis of Sex,” directed by Mimi Leder from a screenplay by Daniel Stiepleman (Justice Ginsburg’s nephew), is interested in Ginsburg’s role in bringing about this change. Rather than trace the full arc of her career, it focuses on the first sex-discrimination case she argued in federal court in the early 1970s, and on the development of a legal strategy to challenge injustices so deeply ingrained as to seem perfectly natural.