For many of us, hanging art on walls generally involves little more than a tape measure, a pencil, and much guesswork, keeping our fingers crossed that the item will somehow be stable, straight, and perfectly placed. But for David Kassel, the founder of ILevel, an art installation and design firm, the placement of such work is an art in and of itself.

ILevel will come into your home and hang everything from valuable pieces such as works by Manet, Japanese folding screens, or heavy antique mirrors, to family photographs and framed posters you’ve had since college. Armed with a backpack weighted down with MacGyver-like tools and gadgets, Mr. Kassel or one of his eight employees will whisk pieces off the wall, moving them until the optimal arrangement strikes. ILevel’s clients run from well-known designers like Bunny Williams, to celebrities such as David Bowie and Mike Nichols and Diane Sawyer, to Bank of America.

“I think of installation as a collage,” said Mr. Kassel, 48, who founded the company in the mid-1980s. A trained collage artist, he has pieces hanging in private collections and the Hudson River Museum. “It’s intuitive. You need to have a puzzle mentality.” He laughed a little. “I’m definitely working something out here, but I’m quite sure what that is.”

As with any projects involving personal taste, one has to be sensitive. “There’s a little marriage counseling involved, there’s a lot of psychology,” Mr. Kassel said. “People are sometimes apologetic about the art, unnecessarily so. We have our own taste, but when we walk into a space, we get down to work.” And what that work entails, exactly, and how long it will take, can vary significantly. (ILevel charges $50 an hour for each ILevel employee used with a four-hour minimum; how many employees one will need depends on the scope of the project.) “Sometimes 30 pieces can take two hours, while three pieces may be a half a day,” he said, explaining that people might only have a few new works to put up on the wall, but their placement might mean moving the vast majority of other pieces in the space.

Which is exactly what happened when Mr. Kassel and his associate, Scott Wilson, arrived at my apartment. With the exception of the framed posters and knickknacks already up on our walls, my husband and I had scant art to offer as possibilities. I did have several framed photographs I wanted to put up, however, and Mr. Kassel offered to come over and show me ILevel in action.

Within moments of walking through the front door, Mr. Kassel began offering his opinion. He told me that many of the items we had up were placed too high and looked a little lost, as if they were “floating” on our walls. I could see he was right. (Our ceilings are 14 feet high, and I remembered with chagrin arguing with my husband that we should hang things higher to take advantage of the space.)

I handed Mr. Kassel the framed photographs and gave him permission to move other pieces around as he saw fit. Soon he was plucking random objects off our walls – an old family photo here, a 1920s Italian illustration there. He and Mr. Wilson would lay the pieces first on the floor, in the arrangement in which they were envisioning for the wall, swapping one photograph or piece of artwork for another, trying to find the best possible placement. “It’s like trying to solve a jigsaw puzzle without the pictures,” Mr. Wilson said.

“You have to consider the possibilities,” Mr. Kassel said. “How do you know how much salt to put on a hamburger? You try it out, you taste it.”

Once they had decided on placement, the duo moved quickly to install, reaching into Mr. Wilson’s deep backpack and pulling out myriad tools such as levels, a cordless drill, a tape measure, wires, and screws.

In less than an hour, they had re-hung about a half a dozen items and placed another six photographs in a tight, salon-style arrangement with room above and on the sides to allow for additions. Each item was secured tightly with two D-rings on either side of the work to keep it from shifting, rather than one hook in the center.

All of ILevel’s employees are artists in their own right, and such installation is a skill they acquire early in their careers. “Nobody’s going to hang that first little show for you,” said Mr. Wilson, 35, a painter who has been working at ILevel for six years. “You figure out how to do it.”

And these are skills that are not easily acquired. “Yes, you could do all this on your own,” Mr. Kassel said. “You could also probably fix your car on your own, too, but why would you?”

ILevel, 212-477-4319, www.ilevel.biz.