For years, a rare breed of projects—designed for the public good—has earned acclaim and even a minute amount of actual criticism in design publications worldwide. Think bus shelters, community gardens, mobile clinics, street art, and the like. Many such projects are featured in this exhibition, or would have qualified to be included in it, since they intervene in social systems, often spontaneously.

This was absolutely the case with ScrapHouse, a temporary demonstration house made entirely of garbage, designed in 2005 by Public Architecture, the nonprofit where I used to work. The house was built in front of San Francisco City Hall in conjunction with World Environment Day.

To be generous, it was a stunt, and the process was challenging. As I traveled throughout the United States, speaking about ScrapHouse in the months following its short-lived existence, I often introduced the project in apologetic terms. This was a house that no one would ever sleep in, set in a city where hundreds or thousands of homeless people sleep on the street or in shelters each night.

My guilt was thus running high when I visited a class of Auburn University students at the Rural Studio in Newbern, Ala. Here were these kids, designing and building real homes for real people in need, often with materials subpar to those we had sourced easily for ScrapHouse.

But a fascinating, unforgettable thing happened when I spoke to these students, which opened my eyes to a totally different aspect of the project. They had routinely been told by visitors to the Rural Studio that they should cherish their projects because they’d never have the chance to do that kind of work again. Yet here we had created an urban project that at least resembled the aesthetic of many Rural Studio homes of the time—a beautiful collage of otherwise disparate materials. It turns out that our temporary intervention had made a lasting impression on those students, on the estimated 10,000 people who visited it, and on me, after all those years.

Fast forward to 2012, and ScrapHouse itself may be largely forgotten, but what we have instead is something far greater: a rapidly evolving field of public interest design. It’s a field and practice that has moved from spontaneous, temporary, and makeshift projects, to lasting interventions of all scales, across the U.S. and around the world.

We’ve seen the rise of game-changing nonprofit design organizations, such as IDEO.org and MASS Design Group—both employing human-centered design to improve public services, environments, and lives. Meanwhile, we have mainstream firms—such as Cannon Design, Pentagram, and Perkins+Will—who are strategically integrating pro-bono design at unprecedented levels. This collective work, and the field of public interest design in general, are premised on a conviction that everyone deserves good design and that every human being needs good design in order to live their lives as best as they can.

We may continue to see a trickle of fantastic public interest design projects, but addressing the bigger social challenges of our time will require breaking from the usual way that designers have long worked: serving the needs of private individuals, as a doctor would a single patient. Instead, we need to start considering the needs of entire populations, especially those who can’t afford to pay.

If I had one wish for this show of spontaneous interventions, it would be to look back in a few years and see it as a prelude to a comparably high-profile showing of even more deliberate, permanent interventions that address the real needs of real people in need. Designers must pursue these larger, more systemic public interest design projects at a scale and a pace never seen before—at a scale and pace that the world needs and deserves. If we’re going to achieve this, today’s designers will need to be far more entrepreneurial and will need to think far more systemically than designers ever have had to before. More than any one building or space, this is the great design challenge of our time.