One day Peter Bogdanovich was at home when Warren Beatty dropped by to make a sandwich. Mr. Bogdanovich’s new book, “Who The Hell’s in It” (Alfred A. Knopf, 528 pages, $35) is that sort of book: Someone’s always dropping in. Mr. Beatty doesn’t even merit his own chapter – he is used as a brief, telling anecdote in the chapter devoted to Cary Grant.

The book, a collection of portraits and conversations with 25 of the more interesting film actors of the 20th century – from Lillian Gish to River Phoenix – is a follow-up to Mr. Bogdanovich’s excellent 1997 collection “Who the Devil Made It: Conversations With Legendary Film Directors.” He has both contexts on his side, having worked with or been friends with almost all of his subjects. And though he stays out of the way of his subjects, his own bumpy career, (from auteur-of-the-moment alongside Scorsese and Coppola to his current status as director of a television biopic on Pete Rose) informs the proceedings perfectly.

In the introduction, Mr. Bogdanovich makes the case for actors as artists. Acting, he points out, was his first love – he studied with Stella Adler at age 16, and he takes the time to review all of his schoolboy productions. He pursued acting until he became a director. And he is now well known for a small role in “The Sopranos.” In the 1960s, as a journalist for Esquire, he made excellent use of his access to actors, interviewing everyone he could. As a director he had a canny sense of casting, giving Carol O’Connor his first leading role in a Clifford Odets play.

A lot of the material here has been published before. Some of it is 40 years old. But none of it feels anything less than fresh, vital, fascinating, and inside, partly because of the quality of the author’s original pieces and partly because he has been so conscientious with the material. Everything has been updated and given a polish – in his chapter devoted to Marlon Brando, he includes a eulogy as coda.

A few of his subjects were less known to him. Humphrey Bogart he wrote an appreciation of several years after his death, Brando he approached for an autograph, and both Lillian Gish and Marilyn Monroe he glimpsed and rubbed up against but never sat down with. That leaves 23 leading lights he knew personally, though some of them – from Grant to James Stewart to John Cassavetes and Anthony Perkins – he clearly had long, close friendships with.

Moving is not a word usually associated with celebrity profiles. In his piece on John Cassavetes, Mr. Bogdanovich recalls, after seeing “A Woman Under the Influence,” his inability to express to the director and his wife Gena Rowlands how powerfully the film had affected him. His interviews with John Wayne and Henry Fonda are so informed, affectionate, and entertaining you only can hope that James Lipton is reading them.

Mr. Bogdanovich’s piece on River Phoenix, who he directed and who appears somewhat out of his league in the company of so many greats, is a particularly touching meditation on talent cut down in its prime. His long and impeccably written piece on Cary Grant, in which he actually evokes the distinctive cadence of his subject, includes one marvelous section in which Grant discloses why he can no longer appear in films (including Mr. Beatty’s “Heaven Can Wait”): Because he’s Cary Grant, and people shouldn’t see Cary Grant as an old man.

In his introduction, having declared his love for film acting as a valid art form, Mr. Bogdanovich makes the rather humble claim that his role is that of an archivist for an art he is devoted to. “To keep the past alive then is among my principal objectives,” he writes. “On the screen, many of these memorable players still breathe, still love. … Why let their lights go out when they have so much to give?”

In these long essays he keeps the flames of fandom, and friendship, alive.

Mr. Georgiades last wrote for these pages on Peter Biskind.