In today’s Mayors’ Panel, moderator Ed Glaeser, author of The Triumph of the City, opened the conversation by asking the four assembled mayors what about Paris they most wish they could take home to their cities. Former Mayor Manny Diaz of Miami, Mayor Sly James of Kansas City, Mayor Boris Johnson of London, and Mayor Ignazio Marino of Rome discussed Paris’ walkability, energy, historic fabric, and many other assets of this great city. Mayor Johnson settled on perhaps the most honest assessment of the matter: “well, we stole their idea for a bikeshare system. But of course, they stole it from Lyon, who stole it from Barcelona. That’s how cities work.”

Cities—or more accurately their leaders–can learn, transfer innovations, and “steal” ideas, but local government budgets seldom include much funding for peer-to-peer learning, travel, or professional development. There are plenty of obstacles to learning from other cities: the legal contexts that cities operate in vary a lot by country or even by state in the U.S. Market conditions vary dramatically among cities. But the easy banter that these four diverse mayors quickly settled into belied those differences and showed just how much common cause cities have across geographies and national boundaries. One ULI Trustee told me that the panel proved that “mayor is a global species.”

The local leaders in every community you’re working in could also benefit from any level of exchange you can support their peers who are innovating in other cities. Just as private sector developers, investors, and designers deeply value face time at ULI meetings to exchange ideas, cities need that networking too. From tax increment financing to supports for entrepreneurship, these mayors traded ideas like kids trade baseball cards. Let’s hope they steal some of those ideas bring them home to their cities. Indeed, as Mayor Johnson said, that is how cities work.