Theatre writer and stage and film director James Lapine, winner of multiple Tonys, a Pulitzer, a Peabody and a string of other critical honors, can now add book author to his resume with the publication this month of Putting It Together: How Stephen Sondheim and I Created Sunday in the Park with George.

An engagingly readable mix of memoir, oral history, show-business manual and script, the illustrated hardback revisits every step that went into the 1984 musical, which won the Pulitzer Prize for drama the following year.

“I wanted to write the kind of book that wasn’t out there,” said Mr. Lapine, as he sat with a cup of iced coffee at a picnic bench outside Morning Glory Farm last week.

“It’s a really remarkable experience, to go back 35 years and talk to people about an event,” he added.

A longtime Edgartown summer resident with his wife, two-time Oscar-winning documentary filmmaker Sarah Kernochan, Mr. Lapine is one of the Island’s most unassuming celebrities, generally going unrecognized around town. But in the world of Broadway musicals, Mr. Lapine is a heavy hitter who, with Mr. Sondheim, followed Sunday in the Park with George with the hugely influential Into the Woods.

Putting It Together unpacks the history of their original collaboration, begun in 1982 when Mr. Lapine was still a relative newcomer to theatre and Mr. Sondheim, two decades his elder, was already a superstar with five Tonys and a string of top shows under his belt — though no recent hits, leaving him open to trying a new collaboration.

“The surprise was that he had seen all three shows I had done, and I had only seen one he had done [Sweeney Todd],” Mr. Lapine recalled last week.

Another surprise was that when Mr. Lapine arrived at Mr. Sondheim’s apartment for their first introduction, the Broadway legend welcomed him by lighting up a joint.

“I didn’t think much about it, was an unusual way to meet someone right off the bat, to get stoned,” Mr. Lapine recalled.

After a long, wide-ranging conversation, the two men continued to meet, considering adaptations of works by Nathanael West and Luis Buñuel before arriving at the notion of dramatizing Georges Seurat’s famous 1886 painting, Sunday Afternoon on the Island of La Grande Jatte.

Having found their subject — with stage set and characters already in place — Mr. Sondheim and Mr. Lapine spent two years developing Seurat’s painting and life story into their musical, gradually involving more collaborators: orchestrators, designers, cast and crew and others even further behind the scenes.

Following a workshop production with actors Christine Baranski, Kelsey Grammer and Brent Spiner in the cast, the show’s Broadway opening in 1984 brought the pointillist masterpiece to life with Mandy Patinkin and Bernadette Peters starring as Seurat and Dot, the painter’s model and lover.

All of these actors, and nearly everyone else involved with the original show (particularly Mr. Sondheim ) spoke with Mr. Lapine as he researched the book. His questions and their answers, transcribed with Mr. Lapine’s notes, make for fast-paced, script-like reading.

In this many-voiced chronicle of how Sunday in the Park with George came to be, we also hear from the music and design team, stage managers, producers, agents, Mr. Patinkin’s wife and Mr. Sondheim’s lawyer.

Along with a 360-degree history of Sunday in the Park with George and the play’s complete book and lyrics, Putting It Together also includes sidebars and footnotes explaining such theatre practices as the difference between Actors’ Equity union contracts for nonprofit and commercial shows.

“It has every aspect a person in theatre should know,” said Mr. Lapine, adding that he hopes the paperback edition will be used as a textbook.

“I think should be required reading for theatre students. No matter what your field is, there are things you need to know,” he said.

But researching Putting It Together proved to be more than a book project for Mr. Lapine — it was a rare opportunity to encounter, from all angles, an experience he only partly comprehended while it was happening.

“There were things I didn’t know (and) a lot of things I didn’t understand,” about such aspects of the production as orchestration and legal contracts, he said. “It’s interesting to understand, in retrospect, what’s going on.”

Mr. Sondheim also had his eyes opened by the book’s accounts of conflicts among Mr. Lapine — the show’s director as well as its writer — and the cast.

“When he read the book, he said to me ‘I’m so glad I didn’t know about all of this other stuff that was going on!’” Mr. Lapine said. “I didn’t talk to him about what I was going through as a director, and it wasn’t pretty at times.”

But as Mr. Patinkin recalls during one of his interviews in the book, Mr. Lapine’s unexpectedly emotional opening night plea to the cast was one for the ages: “You choked the words out, ‘Trust this show. Please believe in what we’ve made,’” Mr. Patinkin tells Mr. Lapine. “You can’t imagine how it ignited all of us.”

Conversations like this one brought Mr. Lapine face to face with his younger self — who leaves him somewhat in awe, he said.

“I’m learning about who I was, not who I am,” he said. “I think to visit your younger self is a real gift. I’m so glad I did it.”

Mr. Lapine is now preparing another Broadway musical, with more than one Vineyard connection. Previews begin in November for Flying Over Sunset, which opens Dec. 13 at the Lincoln Center Theatre. Mr. Lapine developed the work, based on a famous LSD party in the 1950s with Cary Grant, Claire Booth Luce and Aldous Huxley, in part through a residency at the Vineyard Arts Project incubator in Edgartown. The musical’s choreographer is Michelle Dorrance, an acclaimed tap dancer and MacArthur grant winner who has performed at the Yard in past summer seasons.

Mr. Lapine, whose last film as director was Custody with Viola Davis and seasonal Chilmark resident Tony Shalhoub, also recently completed an documentary about Rose Styron, In The Company of Rose.

“I sat down with Rose every summer for, like, six years and filmed our conversations,” Mr. Lapine said. “I love her. She’s so interesting. I just wanted to get her stories down.”