The Metropolitan Museum of Art. The Ace Hotel New York. The Chicago Athletic Association. The NoMad hotel in London. Goop’s store in Los Angeles. The Reykjavik Edition hotel, in Iceland. The Boom Boom Room.

These are all some of the places where people can step into the world of interiors created by Roman and Williams, an architectural and interior design firm started 20 years ago this month. As that world has grown to include locations in seven countries and three continents, Robin Standefer, 58, and Stephen Alesch, 57, the company’s married founders, have often returned to Montauk, N.Y., where they have lived part time since 2006.

“I think this room has been the center of our lives and our creativity for the better part of the past 20 years,” Ms. Standefer said inside a studio at their Long Island home, which they call Sea Ranch, on a Sunday afternoon in October.

In the studio — a renovated garage — there were sheepskin throws covering a wood-frame couch by the Brazilian designer and architect Sergio Rodrigues; bushels of dried hydrangeas bursting from antique battery jars collected by Ms. Standefer; and paintings of seascapes, bought on eBay and embellished by Mr. Alesch, lining a wall. On another wall hung the bust of a stuffed goat, a gift to the couple. Its glassy eyes seemed to be gazing down at a group of conch shells Ms. Standefer had arranged concentrically on a low wood table that she and Mr. Alesch had designed.

“Their rooms are like portals into another place and time,” said Johannes Knoops, a professor in the interior design department at the Fashion Institute of Technology and the chair of the college’s Lawrence Israel Prize committee. The prize, which recognizes exemplary interior design, was awarded to Roman and Williams in 2013.

Interiors designed by Ms. Standefer and Mr. Alesch typically incorporate antiques and vintage pieces meant to be used, not kept out of reach on a shelf. Alexandra Cunningham Cameron, the curator of contemporary design at Cooper Hewitt, Smithsonian Design Museum, said “Roman and Williams have figured out the formula for making antiques physically and intellectually cozy — which, by today’s standards, they most often are not.”

Their process includes researching historical materials and traditional forms of craftsmanship: brick laying, say, or the intricate lost-wax method of casting bronze into decorative objects. The pair often experiments with such techniques themselves, to better understand them, and then works with artisans to apply the methods in their projects, whether pieces of furniture or buildings the firm designs from the ground up.

“There’s no need to reinvent everything all the time,” Mr. Alesch told GQ in 2009, the same year he and Ms. Standefer completed interiors at the Ace Hotel New York, where they filled the lobby with vintage British campaign chairs, tartan-covered armchairs, an enormous American flag and a case of stuffed birds, all lit warmly with filament bulbs. Interior Design magazine honored the Ace in New York as the boutique hotel of the year in 2009, and Wallpaper magazine’s 2010 Design Awards recognized it as one of the five best new hotels.

Once Upon a Time in Hollywood

Roman and Williams Buildings and Interiors, as the firm is formally known, was named for the founders’ maternal grandfathers, William Winters (hers) and Roman Alesch (his). Ms. Standefer and Mr. Alesch started it in the living room of their East Fourth Street loft in Manhattan in November 2002. They first met a decade earlier, in Los Angeles, while working in the art department of the film “The New Age.” Together, they refashioned a storefront on Robertson Boulevard into a fictitious clothing boutique featured in the movie.

Mr. Alesch, who was born in Nina, Wis., grew up in Malibou Lake, a residential community developed by the director Cecil B. DeMille in Agoura Hills, Calif. He studied philosophy and engineering at Northern Arizona University in Flagstaff and apprenticed at architectural firms in Los Angeles before getting into movies. As a set designer, he began each project with a hand drawing, a method he has continued to use at Roman and Williams.

Ms. Standefer, who was born in the Bronx and raised in Manhattan, studied art and architecture at Smith College in Northampton, Mass., before graduating from Hampshire College in Amherst, Mass. She then worked as a curator and, in the late 1980s, as a visual consultant on the film “New York Stories.” In that job she met Martin Scorsese, who later hired her as a creative consultant on his films “Goodfellas” and “The Age of Innocence.”

The pair bought the loft where they would eventually start Roman and Williams in 1997. By then a couple, they would spend time in New York between production design jobs in Hollywood, where they had developed a reputation for craftsmanship, attention to detail and fashioning sets with a lived-in quality that resonated both on and off screen.

“People said that their homes looked fake, and the sets they were on felt real,” Mr. Alesch said. Ms. Standefer added, “The stars and producers on these movie sets said, ‘Why don’t our houses look as good as the movie sets?’ And we were like, ‘They can.’”

Their first high-profile client was the actor Ben Stiller, whom Ms. Standefer and Mr. Alesch had become friendly with while working on the sets of “Zoolander” and “Duplex.” Mr. Stiller hired them in 2002 to redesign his 1920s Spanish-style home in Los Angeles, where they had walls repainted in aquamarine blue, aubergine velvet sofas installed and dark wood bookcases built to match new exposed-wood ceiling beams. In 2003, they opened the first Roman and Williams office in a warehouse on the Paramount Pictures lot in Hollywood.

Their transformation of Mr. Stiller’s home stood out to one visitor in particular. “I walked into Ben’s house, and I was like, ‘Who did your house?’” the actor Kate Hudson said. She had recently bought her childhood home in the Pacific Palisades section of Los Angeles, which was built in the 1930s for the “Frankenstein” director James Whale.

“I was drawn to how specific their eye was,” Ms. Hudson added of Ms. Standefer and Mr. Alesch, whom she hired. “I think that must have come from them working in film. You’re telling a story about who a character is and why they live there.”

After Ms. Hudson and the designers imagined what her house would look like if it were in Morocco, Ms. Standefer and Mr. Alesch decorated it with custom screens incorporating mashrabiya, a type of carved wood latticework native to North Africa and the Middle East, couches and ottomans upholstered in embroidered white silk, and a black Murano glass chandelier.

While working on Ms. Hudson’s home, the duo decided to move to New York. They closed their office on the Paramount lot and in 2004 opened their current office on Lafayette Street in SoHo (which they said would soon move to a different location in the neighborhood). A year later, in 2005, Ms. Standefer and Mr. Alesch were married.

Taking Off in New York

Not long after their pivot to private residences, Ms. Standefer and Mr. Alesch took on a more public-facing project: reimagining the lobby of the Royalton hotel in Midtown Manhattan, which at the time featured interiors designed by Philippe Starck. The lobby became a place to see and be seen after Mr. Starck redesigned it in 1988, but over the years had lost its buzz.

Their Royalton lobby, which featured dark wood paneling, brown leather couches and steel coffee tables, debuted in 2007 to mixed reviews. “The old lobby was the must-see interior of its time, and the new one isn’t,” the critic Alice Rawsthorn wrote in this newspaper.

But by then Roman and Williams had already been hired for other hotel projects. The developer André Balazs, after meeting Ms. Standefer and Mr. Alesch in 2004, commissioned the company to design all the interiors at his first Standard hotel in New York: the Standard, High Line, in the meatpacking district.

Though Roman and Williams had done a hotel lobby, the Standard project was on a different scale. The company at the time had six employees, including its two founders. When told that developers had to visit the office to ensure the firm could do the job, Ms. Standefer recalled thinking, “We need more people.” She added, “So we bring in friends, like to sit in the office, walking through the office.”

A few months after Mr. Balazs hired the firm to do the 338-room Standard hotel, Alex Calderwood, a co-founder of the Ace Hotel chain, commissioned it to design interiors at the Ace Hotel New York, a 258-room property inside a 1904 building formerly known as the Hotel Breslin, in the NoMad neighborhood of Manhattan.

The 2009 debut of both hotels — the Standard that March, and the Ace that May — helped establish Roman and Williams as a design firm with range. The Boom Boom Room club atop the Standard, with its curvy banquettes, glossy golden bar and panoramic view of a shimmering city at night, conveyed 24-karat glamour. The rooms at the Ace, decorated with Gibson guitars and vinyl LPs, evoked hipster sophistication.

Business took off from there. Over the next decade, as Roman and Williams worked on private residences, it took on dozens of public-facing projects: the Manhattan restaurants the Dutch, Lafayette and Le Coucou, as well as restaurants in Paris, Milan and Istanbul; Freehand hotels in New York, Chicago and Miami; a dining hall at Meta’s headquarters in Menlo Park, Calif. (Ms. Standefer and Mr. Alesch never worked directly with Mark Zuckerberg, but they said he was “invoked often.”)

Last year, the company debuted its first hotel projects in Europe with the openings of the NoMad London and the Reykjavik Edition. This summer, the firm completed its most recent project: the 53,000-square-foot Tin Building, a market and food hall conceived by the chef Jean-Georges Vongerichten, in Manhattan’s South Street Seaport. The workload can be demanding, said the company’s artistic director, Tanya Jonsson, who is one of some 50 people now working at Roman and Williams Buildings and Interiors.

“It’s an intense place to work — we have a lot of projects, and we’re super busy,” said Ms. Jonsson, who joined the company in 2012 as an interior designer. “We demand a lot of everyone,” she added, noting that her colleagues are generally “fans of the work and really excited to be part of the journey.”

Art Inspires Commerce

After putting its stamp on clubs, hotels, restaurants and residences, Roman and Williams in 2014 was hired by the Metropolitan Museum of Art to renovate and redesign the museum’s British Galleries: 10 rooms filled with British decorative arts and objects — teapots, silver cutlery, brown furniture — made from 1500 to 1900.

“I used to say no one ever walks through the doors of the Met saying, ‘I want to see the British decorative arts galleries,’” said Luke Syson, one of the curators who led the project and now the director of the Fitzwilliam Museum at the University of Cambridge.

One tactic that Ms. Standefer and Mr. Alesch used to lure visitors: displaying objects in a way that makes them seem less like antiques at a museum and more like products at a store, to encourage browsing.

The British Galleries, which debuted their Roman and Williams makeover in 2020, now feature items in glass display cases much like those used to showcase jewelry or other trinkets at stores. One towering case contains some 130 teapots, which are arranged on glass shelves that invite passers-by to look at the manufacturer name stamped on the bottom of each piece.

“In a way, it’s a very department store tactic,” Mr. Syson said.

While working on the galleries, Ms. Standefer and Mr. Alesch dove deep into the history of Britain’s guilds of traders and craftspeople. The process sparked the idea for Roman and Williams Guild, the retail store they opened on Canal Street in Manhattan in 2017. Last November, they expanded their retail footprint on Canal Street to include the Guild Gallery, which exhibits larger artworks for sale.

More than $5 million, a mix of their own money and funds from investors, was spent to create the Guild gallery, store and its on-site French restaurant, La Mercerie, designed by — yes — Roman and Williams.

At La Mercerie, patrons can eat niçoise salads and mushroom quiches off plates that are for sale nearby in the store. (Also for sale: the restaurant’s forks, knives and drinking glasses.) In addition to selling a namesake RW Guild line of items designed by Ms. Standefer and Mr. Alesch, the store stocks pieces made by independent artisans.

“I think it brings a lot of value to the items that you can see them presented with these beautiful and delicious foods they have,” said Perla Valtierra, a ceramist in Mexico City whose plates are used at La Mercerie and sold at the Guild.

Artisans like Ms. Valtierra do not have to pay for space in the Guild store; Ms. Standefer and Ms. Alesch buy products from individual makers, some of whom receive advances to help fund production. Artists invited to show works at the gallery receive about half the profits from each sale.

Designs for the Future

“Roman and Williams to us was always more an idea than a design practice, and a design practice didn’t satisfy the whole appetite,” Ms. Standefer said over croissants at La Mercerie on a Thursday morning in October.

She and Mr. Alesch have not lost their taste for the interior design work they built their business upon, but after two decades, they have become more selective. “We’re grateful to now be at a level where we can pick and choose our projects,” Ms. Standefer said in an email, noting that in 2021, the year the company completed the NoMad London hotel, it also designed a birdhouse at the Brooklyn Botanic Garden. “We like that and are interested in that mix.”

They just released the OVO collection, a new line of made-to-order furniture sold at the Guild, which includes a curvy oak dining table and chair. Soon to come are the Seed and Branch series, which will include a bronze candelabrum and other décor made using the lost-wax casting process, and the Dado collection, which will include a desk and other furniture inspired in part by Donald Judd’s designs.

Other in-the-works projects include a private residence and artists’ retreat in Montauk for the gallerist David Zwirner and a hotel in Amsterdam. There are hopes to introduce more Guild locations. Mr. Alesch dreams of designing a high school. “You’re constantly looking for what’s missing,” he said.

But first: a party. On Wednesday, Ms. Standefer and Mr. Alesch will celebrate their 20th anniversary in business at the club they designed atop the Standard, High Line.

“We’ve never had our own party at the Boom Boom Room,” Ms. Standefer said. “It’s fantastic.”