Casting Emily Blunt in “Sicario” went something like this: Four weeks after she’d given birth, director Denis Villeneuve sent her the script, and then later met with her while she was dressed in pajamas.

Jeff Daniels was working on HBO’s third and final season of “The Newsroom” when creator Aaron Sorkin began writing “Steve Jobs,” and as Daniels recalls, “I threw my hat into the ring. My audition lasted three years.”

Jason Mitchell Skyped with “Straight Outta Compton” director F. Gary Gray for over an hour, crying and laughing. He didn’t even know he’d landed the part of Eazy-E until after several more days of specialized testing with possible co-stars.

Brian d’Arcy James went from meeting director Tom McCarthy to a table read with the rest of the cast of “Spotlight” less than three weeks later. “We had about four days of rehearsal, and two of those days I stared at everybody wondering how I got there,” he says. “I went from zero to 60 in a matter of two phone calls.”

Casting ensemble films such as “Spotlight,” “Steve Jobs” “Straight Outta Compton” or “Sicario,” is a complex process — partly because what actually makes an “ensemble” film is a matter of debate among casting directors.

“I view every film as an ensemble piece,” says David Rubin, casting director for “Trumbo,” echoing a common sentiment. “When the dayplayer who has one or two lines is 30 feet high on a movie screen, they are the star of the movie in that moment.”

IT TAKES A VILLAGE: “Black Mass,” “The Big Short,” and “Hateful Eight” all feature starry casts.

“Even when a movie is specifically an ensemble, you’re still trying to make a world where everyone feels like they fit in that world,” says “Bridge of Spies” casting director Ellen Lewis. “I enjoy casting someone who says one word as much as I like casting a lead. Every person matters. Every face matters.”

Yet no matter what the film’s subject is, the casting process is a crucial step in making it work — not just for audiences or producers, but also among the collective of actors. Casting directors have a number of go-to ideas for finding the right pairings, and may end up dealing with a group of veterans who can headline their own films, or a collection of beloved character actors, or a ring of newcomers — or some combination of all three.

“It’s like creating a mosaic; you make sure every piece fits perfectly with the surrounding pieces,” says Fiona Weir, who cast “Suffragette,” “Brooklyn” and “Room” this year. “It’s a marathon, not a sprint — it’s many weeks or months of carefully putting together different actors.”

Because casting does involve so many tiles of a mosaic, it’s tough to declare that there is any one “best” method of assembling actors, who often come with disparate styles, approaches and backgrounds. Weir, who cast Irish and American actors for “Brooklyn,” says Americans tend to have a more naturalistic approach to acting, while Europeans are more theater-based and stylized.

“I had to cast actors who were truthful and authentic to their countries, but the film as a whole also had to work,” she notes. “There couldn’t be a whole different style of acting between the two.”

It’s not unusual for casting directors to begin with anchor actors already in place. For “Spies,” Lewis came on board after Tom Hanks was already attached and Mark Rylance was having conversations with director Steven Spielberg. Those hires, she says, helped her decide how to focus on the rest of the film’s casting.

“It’s like, here are two pieces of this world, and I get where we’re going,” she says. “Knowing Tom was in it helped me hone in on Amy Ryan.”
Francine Maisler — who cast ensembles for several awards hopefuls including “Sicario,” “Black Mass,” “Steve Jobs,” “The Big Short” and “The Revenant” — came on board with many of her anchor leads already in place. But for the rest she threw out a wide net on each film. “We often begin by putting up a board with the roles to be cast and a large group of actor photographs,” she says in an email. “It is a lot like putting together a complicated puzzle.”

“I enjoy casting someone who says one word as much as I like casting a lead. Every person matters. Every face matters.”
Ellen Lewis

In many cases, the pieces of that puzzle don’t personally meet until they’re already in place and contracts are signed. On the one hand, veterans are likely to know how to work together well on camera without having actually having been tested with other actors. But on the other, casting directors aren’t usually afforded the luxury (time or budgetwise) of getting top actors to do test reads before any contracts are signed.

That’s often where the director comes in handy. “Actors at the level of the cast in ‘Spotlight,’ you use your sixth sense,” says Paul Schnee, who with Kerry Barden cast the film. “A lot of the credit goes to Tom (McCarthy, the director), who had the foresight to know who goes together.”

“Some of it is luck,” admits “Youth” director Paolo Sorrentino, who wrote his film specifically with Michael Caine in mind for the lead. “Some of it is when you meet the actors one by one, you realize they’re the right person you had in mind for the role.”

That doesn’t mean the c-word — chemistry — doesn’t sometimes get testing. Mitchell was the result of a search for “Compton” that stretched out over years. After he landed his role, he was asked to do three days of chemistry reads with potential co-stars.

“There were three there trying to be (Ice) Cube, and four guys trying to be (Dr.) Dre,” he recalls. “It was three days of scene after scene, really just trying to bang it out. We did different mixes of people to see what would be a real camaraderie.”

“These actors are for the most part emerging into a field where they’re not known quantities,” says Cindy Tolan, who cast “Compton” with Victoria Thomas. “You need to make sure if you are going to spend this kind of money on a film without established actors that you’re getting it right.”

After a certain amount of years in the business, however, many actors don’t have to worry about such chemistry tests — or chemistry at all. “It isn’t something you think into existence, chemistry,” says “Youth” star Rachel Weisz. “It’s something you feel into existence. You have to get out of the way of your heart.”

THE RIGHT NOTE: “Straight Outta Compton” features a cast of mostly unknowns.

But one advantage to having put years into honing your craft and expertise is that the feeling-into-existence part comes more naturally. Put in a room with peers and other performers of their stature, actors know they’re starting out at a professional level, which helps them trust one another more quickly to get into the script.

“Chemistry and great scenes are about the space between two, three or four people,” Blunt says. “We all had different styles (in ‘Sicario’), but we all wanted to make the same film. It felt like a great dance. I’m really interested in people’s idiosyncrasies, and you become willing to do the dance with different personalities. But chemistry is a funny thing between actors — you can find people who work well together, but you can’t bottle it up and sell it.”

What fewer actors will admit is that they size up the rest of the ensemble once they know who their castmates are. “I do that thing where you look around at who’s there, and is someone there just because they’re a hot star right now, or because they’re a real actor,” Daniels says. “This wasn’t the case on ‘Jobs,’ but when it does happen, you cover for mediocrity. You learn how to handle their ‘star school’ stuff and say things like, ‘I need you do it this way for me.’”

To Daniels, there’s little mystery to chemistry. “It’s two actors who are listening to one another,” he says. “That takes openness and trusting of the other actor, which is unusual in Hollywood because we’re all ambitious and making career moves in scenes. If you drop all that and play the scene as two people reacting to one another, suddenly there’s chemistry.”

Regardless of how it happens, assembling the mosaic Weir refers to remains a combination of learned expertise on the part of directors, actors and casting directors — and a little bit of luck. In the end, casting directors have to be almost 100% sure everything will work — long before they ever get to see the film.

“You hope,” says Lewis about making everyone fit well together. “You keep your fingers crossed. It’s a wing and a prayer. Casting is the tricky craft, because what we’re doing is dealing with human beings, so it’s important to be sensitive to our process, and it’s why it doesn’t get acknowledged as much. It’s about people, and you never want to talk about who didn’t get a part. It’s not like a piece of clothing.”