The playgrounds that Aldo van Eyck designed between 1947 and the mid-1960s in Amsterdam are famously beloved—not only because they were designed by van Eyck but because they were initiated by the people of Amsterdam and made possible by the civil servants of the city’s Public Works Department under the enlightened directorship of the great Dutch urbanists Cornelius van Eesteren and Jacoba Mulder. What began as the harmonious participatory relationship between the people and the civil servants of the city and ended up as official planning policy is what gives these recreation areas a unique place not only in the history of playgrounds but also in the history of social democratic government and welfare state politics.

Spontaneity played a big role. How the post–World War II Amsterdam playgrounds came about has become legendary. Mulder was on her way to work one day and noticed that the children in her neighborhood had to play in the dirt in the square in front of her apartment. The first thing she did at the office was to demand that van Eesteren plan a playground there. Aldo van Eyck was a young employee and was given the task of designing it. Once the playground was completed, a neighbor saw the playground and sent a letter to van Eesteren requesting a playground on her street. And so forth and so forth for the first few hundred. Before van Eyck was done he had designed all the play furniture and laid out nearly 1,000 playgrounds himself.

But without a responsible municipal government this would have been impossible. Ingeniously, it transformed terrible circumstances into opportunities. The job, which the municipality set for itself at first, was to find small, unused, derelict lots, many of which had been occupied by Jewish homes and ransacked during wartime. On these demolished foundations, playgrounds were built as cheaply as possible. Eventually the ad-hoc participatory process was made into policy by van Eesteren when new postwar towns outside of Amsterdam were built to accommodate young families. It is in these new towns that more playgrounds were built than anywhere else in Holland. In order to get one, people had to send a request to the Public Works Department. Imagine if every city in the world operated this way?

This ad-hoc process that became policy was carried out according to what I call the PIP principle—participatory, interstitial, and polycentric. Taken as a whole, the Amsterdam playgrounds may be seen as a tightly woven net of public places, knitting the city into a unitary urban fabric and creating a citywide feeling of community.

Is the PIP principle still relevant to cities today? I believe so. I hope that the urban interventions featured in Spontaneous Interventions have an enduring impact. They stand a good chance to do so if they invite the participation of the residents who are affected by the action, take full advantage of overlooked spatial opportunities, and are conceived not so much as stand-alone projects and one-offs but as a part of a larger network of public-space enhancements distributed throughout a city. Only a municipal government can carry this out. Good design is important but good government even more so.

Interventions like these have helped immensely to make Amsterdam the humane city it is today. But the playgrounds make up an infinitesimal part of a larger social democratic urban planning policy, involving access to good public transportation, good schools, good hospitals, good drinking water, and good policing. Without these things, playgrounds become quick fixes, band-aids on bigger problems and perhaps little more than tax-deductible public relations opportunities for a one-percenter philanthropist.

These sorts of interventions are easily translatable to cities all over the world. I have taken PIP-driven playgrounds to Rotterdam and Vienna, as well as to cities in China and Brazil. One project, for the orphaned children in the earthquake-devastated Chinese city of Dujiangyuan in Sichuan Province, was chosen to be part of the Shanghai Biennale in 2010. There seems to be no limit to the number of wonderful ideas emanating from the ground up, but the big question remains: How are they being received from the top down?