DOUGLAS GINSBURG, Federal Judge, U.S. Court of Appeals, D.C. Circuit:
There are now nine justices on the Supreme Court. To rule on a case, at least six justices must participate. A majority of at least five justices determines the outcome.

Justices need not attend the Court to participate. Instead they may listen to recordings and read the transcripts of the arguments.
The Court’s annual term begins the first Monday in October and runs until the next October. From October through April, the justices hear oral arguments. As a rule, each side gets thirty minutes to make its case. No witnesses are called because the Court is reviewing the decisions of lower courts, where witnesses were already heard.
The Court announces its decisions as they are made – as early as October, and usually ending in June. The justices keep working over the summer, considering which cases to review in the next term and preparing for them.
Before issuing an opinion, the justices and their clerks do a lot of writing. A single opinion might go through a dozen or more revisions. One justice might write a single opinion for the majority. On the other hand, each justice in the majority might write a separate opinion. The justices may reach the same conclusion but for different reasons. The same procedure holds for dissenting justices.
If there are several opinions, it can be difficult to decipher an over-arching principle from the judgment. What counts, of course, is the result: which side a majority of five or more justices agreed with.
Under the Constitution, the decision becomes part of the law of the land, binding on all other courts.