At a Harvard Law School event a few weeks ago that honored Alan Dershowitz’s career, Larry David sent a video. “Look, the world is divided into two groups of people,” Mr. Dershowitz said, quoting Mr. David, an actor and fellow seasonal Vineyarder. “There are people who don’t know Alan and hate him. People who know Alan and love him. I’m in a third category. I know Alan really well and I hate his guts.”

“He went on to compliment me, of course, but he took on the division of people who know me and people who don’t know me,” Mr. Dershowitz said.

Mr. Dershowitz is well known as the “Dersh,” a successful defense lawyer, television commentator and Harvard Law School professor who has been involved in some of the late 20th century’s most famous court cases. He has worked on defense cases for O.J. Simpson, Mike Tyson and Claus von Bulow, to name just a few.

But then there’s what he calls the “Vineyard Dershowitz,” a more personal side that he conveys in his new book, Taking the Stand: My Life in The Law. This Dershowitz is a family man, an avid Red Sox fan — he has thrown out the first pitch at a game and had a pastrami sandwich at the Bleacher Bar named after him — and a guy who likes to shoot the breeze on the porch of the Chilmark General Store.

“You may think you know the Dersh character from television but the real Alan is a different person,” Mr. Dershowitz said during a phone interview last week. “I try to expose my readers to both sides of my personality . . . so people get to know a different side of me, more the Vineyard side of me.”

On the Vineyard and off, Mr. Dershowitz is a busy guy. He just turned 75, and is in his 50th year of practicing law. Taking the Stand is his 30th book.

“I just thought it was appropriate to write a memoir which summarizes and relates my private life to my public life,” he said. “People know me publicly as the Dersh character, the guy who’s always talking on TV and that kind of thing. What people don’t know is the personal me.”

The book pairs the two Dershowitzes side by side, recounting his childhood in Brooklyn, where he was a poor student (a picture of his report card proves it), to his later success in academia and the courtroom. Discussions about court cases and legal issues including the first amendment and the death penalty are paired with vignettes about his family life, his encounters with celebrities and his life on the Vineyard.

“I don’t engage in false modesty,” he said. “I take credit where I think I deserve credit. And I think I also take blame where I think I deserve blame, so I try to do a little of each.”

It was the law, in fact, that first brought Mr. Dershowitz to the Vineyard. He was part of the legal team that represented Sen. Edward Kennedy after the 1969 fatal car accident on Chappaquiddick that killed a young woman, Mary Jo Kopechne. Mr. Dershowitz worked on a brief about the privacy rights of women who were called to testify at an inquest into the matter, and Mr. Kennedy eventually pleaded guilty to leaving the scene of an accident.

“I am still not free to disclose everything I know about the case,” Mr. Dershowitz wrote in the book. But he can share his first impression of the Vineyard. “I hated it,” he said last week.

He stayed at the Kelley House and never left Edgartown, he said. He recalled being pushed and shoved during the media frenzy and “I swore I’d never come back.”

But the next summer, Anthony Lewis, the late Pulitzer-prize winning legal journalist, put out a notice to Harvard Law School faculty that he was renting his house on Deep Bottom Cove for “the outrageous and unaffordable price of $100 a week,” Mr. Dershowitz recalled. Mr. Dershowitz chipped in with his brother to spend three weeks on the Island. This trip was much better. He’s been back nearly every year since, now owns a home in Chilmark, and has become a summer fixture on the Island.

“I probably do 60 per cent of my yearly writing in the 10 weeks that I’m on the Vineyard. I get up early in the morning and I work pretty much straight through until exactly 11:45 a.m.,” he said. “At 11:45, no matter what, I leave my house and I go to the Chilmark porch for lunch with my buddies [Mr. David among them]. And we sit there, we tell the same old jokes and gossip. We never talk about anything too serious, mostly it’s Vineyard news, and that’s what I do about every day.

Alan Dershowitz with daughter Ella and wife Carolyn Cohen. — Peter Simon

“The porch of the Chilmark Store costs me at least five pounds a year because of the great pizza that I eat,” he added. “I usually have a slice of pizza for lunch and I shouldn’t. I do, it’s too good.”

As a counterbalance, he said he also walks five miles a day on the Vineyard. He spends the rest of his time with family and friends, and going to the beach and fishing. His birthday and his anniversary fall during the summer too.

But the Vineyard Dersh is still Dershowitz, after all, and he said he can’t say no to a request. He speaks at the Chilmark Library, the Chilmark Community Center, the Hebrew Center and at forums hosted by Henry Louis (Skip) Gates Jr. and Charles Ogletree. He donates a dream (usually Red Sox tickets) to the Possible Dreams Auction and his living room is filled with artwork from Vineyard artists.

He said the Island’s appeal is a combination of physical beauty, intellectual stimulus, relaxation and anonymity.

“On the Vineyard everyone leaves you alone,” he said. “You’re not Professor Dershowitz, you’re the guy on the Chilmark porch or the guy on the beach. So you can be yourself. You’re not somebody who is known for his profession or his celebrity, you’re just the guy on the porch. I love that.

“I’ve said often, if the whole world were like the Vineyard, you wouldn’t need Google. When I walk down the beach or I’m on the porch I don’t have to look anything up, there’s always an expert I can ask.”

Mr. Dershowitz said he tries to stay out of Vineyard legal cases, though he once defended someone who off-loaded a bunch of marijuana on the beach at Gay Head. “And we got a good deal for him,” Mr. Dershowitz said. His client spent a month in the Edgartown house of correction.

On the Vineyard, the issues are more personal. “I have my own case. One year somebody stole the motor off my boat,” Mr. Dershowitz said. “I found out it was one of the people in our pond association who didn’t like where I was parking my boat, so he stole the motor and then returned it at the end of the summer.”

Mr. Dershowitz, the famous litigator, did not press charges. “I just wanted to expose him . . . he stole the motor off my boat and he’s a jerk,” he said. “He’s lucky I didn’t go after him.”

Mr. Dershowitz is so much a Vineyard fixture that during early preparations for President Obama’s visit this summer, the work was done under the code name “Alan Dershowitz’s birthday party,” a tidbit recounted in his book. While the president did not attend the actual party, he did send a note, Mr. Dershowitz said, wishing the professor continuing happiness and mischief.

When he looks back, “what surprised me is that I ever got anywhere in life!” Mr. Dershowitz said. “I was a bum in high school . . . I was a terrible, terrible student and people thought I would never amount to anything. So what surprised me is that I’ve had a successful career and I had something of an influence on American law. That is the biggest surprise. I come from a family where no one went to college, and . . . within one decade, I changed from being one of the worst students in a mediocre high school to being the youngest professor in the history of Harvard Law School.”

It’s hard to know what changed, he said, but he pointed to a few things. “First, I grew up a little bit,” he said. “Second, I met a woman who I eventually married. Third, a few people told me I was smart, and fourth, I probably wanted to show those guys in high school that I wasn’t nearly as dumb as they thought I was.”

With all his cases, one stands out, he said: the defense of Anatoly Sharansky, a Soviet dissident who was sentenced to death by the Soviet Union for a charge of spying for the United States. Mr. Dershowitz represented Mr. Sharansky, as recounted in the book, and eventually secured his release.

“I really strongly identify with that case because there but for the grace of God — and my parents’, my grandparents’ wisdom — go I. I mean if my parents had made a right turn and gone to Russia during the early 20th century and his parents had come to America, we might be in different situations. He might be the lawyer and I might be the dissident. So I had a close personal identification trying to free him from the Soviet gulag.”

Mr. Sharansky now lives in Israel and has two children. Mr. Dershowitz said he still keeps in touch with him.

Mr. Dershowitz’s book ends with a letter to the editor that can run after his obituary. He said he’s picked out his burial spot: Abel’s Hill cemetery, with an eternal view of the ocean.

But he still has lots to do. Mr. Dershowitz tries to stay on the cutting edge of legal developments, he said, and uses science in the courtroom. He advocates for law school reform, making the third year a clinical year.

He was brought to Harvard Law School as a law and social sciences professor, and he said he’s spent the last five decades trying to broaden students’ horizons, emphasizing that the law is interdisciplinary. He’s now teaching a course on the law and Shakespeare, and last year he taught a course on the law and baseball. “The students I’m teaching now will be practicing law 50 years from now. So I’m trying to teach them about how to be good lawyers when I’m long gone. For a teacher that is life after death, the world to come.

“That’s the great legacy that every teacher dreams for, to have a continuing impact through your students,” he said.

This year marks Mr. Dershowitz’s last one teaching at Harvard, though he said he’ll still make the occasional appearance or teach a freshman seminar. He hopes to focus on his writing and litigating.

He’s still involved with several cases, he said, including several murder cases and representing the former president of Pakistan, Pervez Musharraf. He recently won acquittal in the murder case of the former president of the Ukraine, Leonid Kuchma.

“I’m busier than I’ve ever been from a career point of view,” he said. Come next summer, he’ll continue work on his next book, a look at lawyers throughout history. He begins with the biblical character Abraham and goes through time to Abraham Lincoln and Mr. Dershowitz himself, whose Hebrew name is Abraham.

“I call Abraham the world’s first lawyer because he argued with God over the sinners of Sodom,” he said. “He was also the first lawyer ever to argue for gay rights, because the people of Sodom were believed to be engaging in homosexual behavior and that’s why God was going to punish them. And Abraham rejected that view.”

Given the breadth of his legal experience, were there any cases that got away?

“I would’ve loved to defend Jesus back 2,000 years ago,” he said, while giving directions to a cab driver. “Wouldn’t that be great for a Jewish lawyer to win acquittal for Jesus, that’d be terrific.”

He thought some more and referred to a legal case that was in the news that day. “I wish I could have been involved in the Skakel case,” he said, referring to Michael Skakel’s murder trial. “I think I would have done a better job than his lawyer did."

“But mostly, almost every major case that’s been around in the last 50 years I’ve had something to do with,” he said. “So I’ve been very fortunate that I’ve been at the center of so many cases and controversies.”