Architect Gustavo Costa calls the home library the “project’s heart.” This central space houses the owner’s expansive collection of about 5,000 books, and acts as a meeting place for friends and colleagues. A Gerrit Thomas Rietveld Red and Blue chair completes the space.

The studio’s second floor serves as a library. The sunken bathtub offers interrupted sightlines across the space and out into the backyard. The tub, like the library’s floor, is made of concrete.

One of the greatest design challenges, according to Franz and Paré-Mayer, was reimagining the dark, unfinished garage space in a way that would “establish [it] as primary, instead of an afterthought to the original floor above.” This was achieved by layering open, linked spaces on the ground floor and sticking to a few carefully selected materials for cohesion and fluidity. There are hardly any hallways in the home; every space serves a function. Polished concrete floors continue throughout the new living level, and a bent metal dining chair with a reclaimed Douglas fir backrest made by Scholz sits in front of an open white oak staircase.

Located in West Village, designer Suchi Reddy constructs a modern family-friendly apartment.

Located on the outskirts of Morelia, Mexico, the 5,920-square-foot UC House by architectural designer Daniela Bucio Sistos is grounded by a foyer with a raised, circular ceiling, which houses a tree that grows out from a hole in the floor at the center.

Floor-to-ceiling bookshelves provide ample storage for books and memorabilia.

The library is lined in reclaimed spotted gum that Maynard says “brings with it wisdom from its previous life.” A stained glass window by Leigh Schellekens makes the contemplative room feel like a domestic chapel.

To impart a high-design feel to the space, architect Mike Jacobs wrapped cabinetry from Ikea with a marble countertop and designed built-in bookshelves around the kitchen and study to help unify the area. Trips to shops in Palm Springs yielded the red side chair and metal magazine rack. The brown suede chair is from MidcenturyLA.

On one side of the house, a white central staircase leads to a split-level landing the Robertsons call "the reading room." "We needed a place to hang out and for the kids to read," explains owner Vivi Nguyen-Robertson. Awaiting the birth of the couple's son, she relaxes in a built-in reading nook in the library.

Vila D’Acosta-Calheiros hung a space-saving wall shelf in the library. The table is by Eero Saarinen; the Tolomeo lamp is by Michele de Lucchi for Artemide. The red beanbag-like Sacco chair is by Zanotta, as is the Sciangai coatrack in the hall, beyond.

Houston-based designer Barbara Hill is known for a stripped-down aesthetic that blends art-world cachet with Texas modernism. Vitra’s Slow chair sits in front of a powder-coated-steel bookcase made by Hill’s go-to fabricator, George Sacaris; it was originally built for the Houston house.

Clerestory windows in Tyler's design studio provide plenty of light, while built-in bookshelves and flat files offer ample storage.

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The couple has a large collection of cookbooks. To provide storage for them in the kitchen—and also seating—Sawatzky topped narrow bookcases (Bestå units by Ikea) with custom-made cushions, upholstered in gray Circa fabric by Knoll Textiles purchased from Modern Fabrics. The bookshelf-cum-bench was custom upholstered by Tina Morgan Designs.

In the ground-floor gallery, 40-foot-long library shelving is punctuated by floor-to-ceiling columns made from white acrylic panels that conceal low-cost fluorescent-tube lighting.

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Tagliabue made sense of the soaring volume in the library by installing double-height custom bookcases that can be accessed via a catwalk.

French doors line one wall that extends from the library to the first-floor sitting room and office.

The architects set up a cozy reading nook off the kitchen, with furnishings picked by Santos. Positioned as it is beside the big windows, the spot benefits from the views outside, and enables family members to chat easily while cooking.

Johan Bouwmeester built a library out of oak.

The stepped wooden platforms provide built-in seats for the library. Down the stairs to the left is a guest room.

Averse to the idea of a television being the centerpiece of a space, the owners instead opted for a clever alternative in the library/media room. Continuing the theme of movable and multi-functional design elements, a rolling chalkboard panel was designed to conceal the TV when not in use. Throughout the home, the family’s furniture is an eclectic mix of purchased, custom built, inherited, and self-made pieces. The room is accented with a reclaimed red office chair with custom white oak armrests made by Scholz.

Custom steel shelving runs in front of two large windows in the bedroom. The designers wanted to keep a thin profile to avoid blocking natural light.

Three’s Company Inspired by the minimal color scheme of a hotel they stayed at in Bali, Winterhalder and Ehlers decided to limit their palette to three colors: anthracite black, concrete gray, and a light larch wood. The first move was to paint the backyard wall gray. Next up for a coat of dark paint was the villa’s old-fashioned wooden staircase, which the couple didn’t like but didn’t have the budget to replace. The consistency works to unite the different styles found in the house. “Somehow,” says Winterhalder, “it all fits.”

The two-story library wall that rises next to the dining area is one of the defining features of the interior. The shelves are made from glulam beams and contain storage along the base that the couple’s three-year-old daughter, Velaug, uses for toys.

A dining room that was converted to a library.

A low shelf in the Uli Wagner Design Lab office houses the studio library as well as an assortment of objets d’art that give the space a unique character.

The library holds a wall-size blackboard for the Bancrofts’ four children, with a colorful permanent piece by local artist Derek Phillips.

Libra flooring outfits the library.

The library is accessed by a sliding wood door.

When he moved in, Judin noticed that his existing furniture fit right into the new space—many pieces are also from the '50s. See more images here.

Due to zoning restrictions, the house's footprint had to be relatively small, so Svensen devised a solution: split levels. The library occupies a landing on the staircase and features shelves built by Atlanta's Dark Horse Woodwork.

The husband is a psychoanalyst who attends to patients in São Paulo as well as in the home—hence the generous proportions of the library and office.

The library is formed simply by two custom bookcases enclosing the space.