He may have a reputation for inscrutability, but Hedi Slimane is actually an open book. Hedi Slimane Diary, an online photographic journal which the photographer and designer has been running on his website for a decade, is a 4,400-image-strong record of his preoccupations and obsessions: from modernist architecture to mosh pits; surfers to street fashion; amplifiers to armpits. Glorious beaches and scuzzy nightclubs are recorded with equal style, affection, and clarity, Slimane’s diamond-sharp eye capturing subjects from ephemera—like the pin badges on a speaker—to historical artifacts, like David Bowie’s platform boots. Entirely monochrome, the Diary is wide-ranging in scope, taking in portraiture and still life, but its predominant mode is reportage—a glorious record of Slimane’s movements through youth subcultures, from concerts to clubs to rodeos. None of it is styled—even the portraits—and there’s no post-production. It’s kinetic, deeply personal, and, Slimane says, “very raw.”

Today, of course, it’s de rigueur to leave a trail of images in real time as you progress through the world, but in 2006—pre-Instagram and pre-Tumblr—it was highly unusual. Back then, high-quality photography was created for consumption in print; the digital realm was viewed with suspicion. Hedi Slimane Diary was pioneering in the way it was conceived as a purely web-based project, Slimane recognizing very quickly that images could be put online almost instantly, free of space constraints and the requirements of magazine editors. “There’s something interesting about the immediacy of the posting and the relevance of it being something of this precise moment, that it exists right away,” says Slimane over the phone from Los Angeles, his adopted hometown. When shooting for a monthly magazine, “it’s a drag that it stays in the fridge for three months…it feels very anachronistic.” Fast-moving, exhilarating and frequently updated, the Diary was a breakthrough and liberation, which quickly inspired others to follow suit—Purple magazine and Terry Richardson for two.

Hedi Slimane Diary was also more farsighted in the way it showed how people would come to communicate predominantly in images online, “which, funnily enough, is what social media became after,” says Slimane. “The idea of just reducing it to semiotics—it could be just a still life, a fragment—that’s something that also was taken up afterwards on social media, before it became selfies.” Before then, an online diary had meant text—a blog—but in keeping with his minimalist aesthetics, Slimane decided to strip everything away, including captions. “I wanted it to leave more to the imagination; I didn’t want to give too many keys to it,” he says. “I felt I had to leave it almost as a rhythmic thing, where it’s very silent because the subject is always pretty chaotic.” Instead, the photographs unite Slimane’s twin loves of high formalism and very human messiness—the tumultuous emotions unleashed by music captured and frozen in time. The Diary moves across the decade from London to Los Angeles, but the passion in the pictures doesn’t change. “We had the English period and then California. In a way they have different sensibilities, a different culture, a different time, but for me it’s still the same youth regardless.”

“I used to spend so much time there in the late 80s and early 90s, which was such a great period in New York. I haven’t been spending enough time to really document it for decades, so maybe I’ll do more things in New York.”

Slimane has been taking photographs since childhood; it is still very unusual to see him out and about without a camera in his hand. Hedi Slimane Diary grew naturally out of his books about Berlin youth and the early 2000s indie scene, and then Rock Diary, a project he and I did together, which over three years documented the explosion of young bands in London. Attending gigs with Slimane in ramshackle venues across the capital, I saw his photographic MO up close. He really gets in the thick of the action—if not actually on the stage, then right in the pit, and when he emerges he’s buzzing. The Hedi Slimane Diary is nothing if not a labour of love.

It is also a record of some of the great talents—and beauties—of the age, a testament to keeping one’s eyes open at all times. However riotous the environment, Slimane will somehow zero in on the most elegant and interesting person in the room, instinctively attuned to personal creativity and style. “The idea of finding a subject, a character in a crowd, I’ve been doing for so long that it’s really immediate,” he says. “The sense of grace—you see it in a crowd and I notice them right away.”

Some faces only appear once in the diary, but others become totemic figures to which Slimane returns: people like Pete Doherty, patron saint of the London scene, photographed with his kittens; Christopher Owens, the soulful, defiantly original San Francisco troubadour; Sidney Williams, the archetypal West Coast blonde Slimane discovered at Coachella; and Jonny Pierce from the Drums, the band who effortlessly grafted together British and American indie rock into something insouciant and fresh. Such characters, Slimane says, are the natural figureheads of the kinds of communities he’s documenting and participating in. “Some characters embody an idea and then they lead their community, either artistically or creatively or just in terms of inspiration,” he explains. “Christopher was definitely a key character in the early days of the California period.”