HALF a century ago, on Oct. 4, 1959, an event took place at the Reuben Gallery in the East Village that changed the course of art history: a performance piece by the artist Allan Kaprow titled “18 Happenings in 6 Parts.” It is now known as the first Happening, a mythical event that knocked painting and sculpture from their previously unassailable perches and paved the way for performance art. Within months other artists were mounting their own performances too, including Claes Oldenburg, Jim Dine, Robert Whitman and Red Grooms. The scene flamed out almost as quickly as it had begun, but not before prompting a radical reassessment of the boundary between art and life. But what actually happened at the Happenings? Because they were so ephemeral, and documentation is so patchy, art historians have spent decades trying to figure that out. So have their creators. “It’s very hard to remember,” Mr. Oldenburg said. “If you look at the scripts, you can’t understand anything, and a lot of it changed during the performance. The best record of those days is still photography.” And the most prolific photographer was Robert R. McElroy, a college acquaintance of Mr. Dine’s, who hung out with the artists and photographed their work, until his attention was diverted by his job as a staff photographer for Newsweek. The thousands of images he made languished in storage until about five years ago, when Milly Glimcher, director of special projects at Pace Gallery, finally gained access. The result is “Happenings: New York, 1958-1963,” opening Friday at Pace, at 534 West 25th Street in Chelsea. It includes nearly 360 photographs (most by Mr. McElroy) as well as artworks and ephemera that came out of those events. The catalog is published by Monacelli Press. In advance of the show some of the creators and participants — including Lucas Samaras, now known for films, photographs and multimedia work, and Patty Mucha, a painter and Mr. Oldenburg’s first wife — shared their recollections with Carol Kino, as did Arne Glimcher, the founder of Pace Gallery, who attended several Happenings and is married to Ms. Glimcher. Here are edited excerpts: LUCAS SAMARAS For “18 Happenings” Kaprow created isolated spaces with little constructions in them, a couple of blocks or beams of wood. Then he would put chairs in them, so that people could sit in the same room with something happening. In one room he had a woman sit in front of a table with oranges, just squeezing them. The idea was to see something real happening in front of you and to then imagine it as a special event. PATTY MUCHA To me [Kaprow’s Happening] was shocking, was really mind blowing. It was the tail end of the Abstract Expressionists, and they were kind of boring — all those shows that were going on everywhere — but these artists were just completely alive. SAMARAS The others started making Happenings almost immediately. Whitman’s read as poetry; for Claes it was more connected to the cinema; Red Grooms started doing stuff that almost looked like commedia dell’arte. He would paint his face white, and he was a redhead, so he looked spectacular. RED GROOMS All of us were painters or makers of something. I guess we all had a knack for doing something theatrical, and there was a certain sort of movement in painting at that time. Pollock was a prime influence, with his all-out gestural approach and his innovation of putting the canvas on the floor. There were poetry and jazz sessions too that became a kind of theater. You could get out on the stage without having to do traditional acting. Inspired by Kaprow, Mr. Grooms had already put on “Walking Man,” his first Happening-like event, that September in a gallery in Provincetown, Mass. Afterward he returned to New York and opened the Delancey Street Museum in a downtown loft. That’s where he staged his second performance, “The Burning Building,” in December 1959. It featured a cast of five, and included two fireman characters. GROOMS I was enamored with all sorts of theater — circuses, carnivals, ice shows, things on television. In high school assemblies I would do skits; I’d come out in a tutu and do a pratfall. So my Happenings were physical as well. In all of them I played this character called the Pasty Man, who would come out from behind the curtains with this candle. In “The Burning Building” one of the Firemen slipped behind me with a sock full of flour and hit me over the head with it. A hand came out from the curtain and took the candle as I fell back into the Fireman’s arms, and he dragged me behind the curtain. More events followed. In January 1960 the Reuben Gallery staged an “Evening of Happenings,” which included Robert Whitman’s first performance. In February, at the Judson Church, Mr. Dine and Mr. Oldenburg organized “Ray Gun Spex,” a series of six performances conceived by themselves and others. Mr. Oldenburg staged his first piece, “Snapshots From the City,” in the Street, an urban environment that he built in the space. For Mr. Dine’s event, “The Smiling Workman,” he dressed like a clown and enacted a performance with paint: stroking it on canvas, drinking it (that paint was actually tomato juice) and pouring it over himself. JIM DINE Claes and I would see each other every night on the Bowery picking up detritus from the street. It was very easy to find things that you could make so-called art out of. But besides wanting to be plastic artists, we felt a need to perform, to make visible the energy that young men had. CLAES OLDENBURG There was nothing especially new about the form; it was how the performances were put together and the thought behind them. My first consisted of Patty and me in costume performing a kind of wild dance while Lucas was offstage in charge of the lights. With Lucas, whatever you ask him to do, he’s going to do it his way. So there were many periods we were in total darkness. GROOMS It was like a sandlot sports game or something, where you just choose sides. Somebody’s the director and makes up the plays, like in football. It’s very improvised, but it’s been directed a bit. DINE My first performance wasn’t some spontaneous act any more than a painting is. I thought it through, I wrote it down. I made some sketches, prepared the set and hoped for the best. I trusted my own sense of drama. I had no idea what kind of reaction I would get, but the reaction I got was so tremendous that it was heavy. SAMARAS The Happenings were crowded, though a crowd could mean 20 people. But it was still magical for us because they responded. In November 1961 at the Reuben Gallery, inspired by President John F. Kennedy’s race to the Moon initiative, Mr. Whitman staged “American Moon,” with six performers, intricate lighting and a set with catwalks. He also made the audience members sit inside six separate tunnels, rough-hewn structures positioned around a central stage, and transformed them into participants. ARNE GLIMCHER Happenings were really a kind of marvelous experience of one’s sense of self, one’s fear of close contact with other people, especially because you were mashed together. People were trapped in those tunnels. SAMARAS All the happenings happened in dumpy places. When artists started moving into lofts, they wouldn’t even clean them. So you went to this groovy place, and it was dark, with a few lights or flashlights. It was a spectacular jolting of your senses. ROBERT WHITMAN Everything about the production was as crude and as primitive as it could be, because nobody really had any money to spend on any of this stuff. And it was generally more visual than traditional theater: the accent was on the plastic composition more than storytelling. MUCHA We saw very little traditional theater. One year Claes’s mother gave us tickets to see “Camelot” for our wedding anniversary, with Richard Burton and Julie Andrews. Claes could hardly bear it. He pretended to be asleep. In December 1961 Mr. Oldenburg moved his studio to East Second Street and opened his installation “The Store,” where he sold handmade versions of manufactured goods. In 1962 he held several Happenings there. MUCHA Claes was indifferent to the comfort of the audience. He’d torment them. In one of the “Store” events Lucas and I did a dance: He picked me up, I serpentined all over his body and chomped on a challah bread and read the comics from The Daily News. We had the entire studio, and part of the audience stood behind a canvas scrim with holes in it, so they could only peek through. I don’t think they saw it all. OLDENBURG The audience was made to suffer. At one performance the only person allowed to sit was Duchamp. He said, “I am very old, and I cannot stand, please let me sit down.” I thought, “Maybe it’s a trick. But then again, he was very old.” I think Duchamp went to everybody’s performances. “Nekropolis I” ended with us all becoming mice, dressed in burlap bags. We crawled out into the audience slowly; we couldn’t see. Then we were supposed to just drop somewhere and not move until they went home. According to the story I wound up on the feet of Duchamp. But I couldn’t see who it was. It’s a good story, but as time goes by you wonder, “Did this really happen?” Because of the transitory nature of the Happenings, the few things left over from them came to be seen as valuable. Some of the props from Mr. Oldenburg’s performances, sewn by Ms. Mucha, became the basis for his soft sculptures. MUCHA I made my first prop for “Snapshots From the City”: a wig with long lollipop curls, made out of black tights that were stuffed and then tied in various places so they looked almost like braids. For “Store Days II” I made some props out of muslin, a sailboat and a freighter, and I did a dance with them. They were later sold to the Guggenheim. They actually became art. Kaprow, who died in 2006, abandoned Happenings in 1963. By then Mr. Dine and Mr. Grooms had already stopped performing, and Mr. Oldenburg was focusing on sculpture. Only Mr. Whitman continued. DINE It was becoming more public. Dealers were beginning to turn up. OLDENBURG At first almost everybody there was someone that you could recognize in the art scene. Then as the performances got more publicity, there came strangers. There was even something called a “thrill club,” organized on Long Island to bring people in for exciting weekends in New York. They would arrive in limos. But they were mystified and mostly disappointed. As time went on, the audience became less and less interesting to me. I couldn’t really reach them. SAMARAS It was a short period, and it was terrific. It was like you had a tribe, a group of entertainers going from village to village with a tambourine. But then you get to a point where you say, “I’m not getting enough out of this.” Everything has a beginning, middle and end, even if you don’t want it to.