Souter and the other members of the high court exchanged traditional letters, personally signed, that struck a particularly warm note for the quiet man from New Hampshire.
Monday was the last scheduled day for the "sitting" of the court in the 2008 term, which began last October.
A letter headed "Dear David," written by Chief Justice John Roberts and signed by seven other court members, said: "We have all felt a profound sense of loss since the announcement of your decision to retire. For nearly 20 years, the court has had the benefit of wisdom, civility and dedication to the cause of justice. ... We understand your desire to trade white marble for White Mountains (of New Hampshire), and return to your land 'of easy wind and downy flake.' ... Affectionately."
In a reply signed "Yours affectionately, David," Souter said in part: "You quoted the poet," Robert Frost, "and I will, too, in words that set out the ideal of the life engaged, '... where love and need are one. ...'
That phrase accounts for the finest moments of my life on this court, as we have agreed or contended with each other over those things that matter to decent people in a civil society. ... I will not sit with you at our bench again after the court rises for the summer this time, but neither will I retire from our friendship, which has held us together despite the pull of the most passionate dissent."
Souter was appointed as an ostensible conservative by President George H.W. Bush in 1990 and confirmed by the U.S. Senate 90-9 to the seat being vacated by Justice William Brennan. Like Brennan, he turned out to be one of the court's liberal lions.
Souter, a 69-year-old bachelor, often asked questions from the bench, but never tried to rattle a lawyer or put an attorney into question whiplash, as did Justice Antonin Scalia. Souter was known for his aversion to high-tech tools -- he's never used e-mail -- and for avoiding the media.
Souter was once observed hanging on to a passenger strap for dear life as Scalia sped his BWM away from the court for a mutual appointment.
President Barack Obama has named U.S. Circuit Judge Sonia Sotomayor to fill Souter's seat.