Ultimately, despite widespread speculation that Stevens would cap his distinguished career by writing the majority opinion in Bilski v. Kappos, Justice Anthony Kennedy wound up as the author of the controlling opinion in the closely watched patent case.
While all nine justices agreed that the “invention” at issue in the case—a method for hedging weather-related risk in energy trading developed by Bernard Bilski and Rand Warsaw—was too abstract to merit patent protection, only four signed on to Kennedy’s opinion.
That opinion held that the "machine-or-transformation" test for patentability--created by the U.S. Court of Appeals for the Federal Circuit in its Bilski decision--was a "useful clue" when gauging a subject’s patentability but shouldn't be considered the only applicable test.
Read More: Court's Opinion (pdf)