The Paris climate summit is a tale of lessons learned – lessons both in how to manage an unruly negotiating process that can easily veer out of control, and in how to craft a multilateral approach that gets everyone to do more.

The tale ended thankfully tonight with an agreement that could prove the most significant turning point ever in two decades of climate diplomacy.

The Paris agreement is a pragmatic deal that delivers what’s needed – tools to hold countries accountable and build ambition over time. By giving countries greater confidence that all are doing their fair share, it will make it easier for each to do more.

I’ve engaged closely with the U.N. climate talks since their launch in 1992, and here are some of my takeaways on the ingredients for Paris’ success:

Expectations are a powerful force

Even before the summit started or a single word was agreed, more than 180 countries had offered concrete plans for how they intend to address climate change. This was not because they were obliged to, but simply because there was an expectation set two years ago in Warsaw that they would.

This unprecedented, and largely unanticipated, show of political will created powerful momentum heading into Paris.

The agreement that emerged sets some binding commitments (see below), but much of its force will hinge on the further expectations that it sets: that, going forward, countries will put forward their best efforts, and will strengthen them over time. It creates a succession of political moments, like the one we just experienced, when all can judge whether those expectations are met.

Be binding, but be flexible, too

The deal is a hybrid.

It includes binding “top-down” commitments: All countries must make contributions to the global effort, report on their efforts, undergo international review, and update their contributions every five years.

But it gives countries wide latitude to define their own individual contributions – they are “nationally determined.” This “bottom-up” flexibility lets countries match their efforts to their circumstances.

That doesn’t guarantee strong ambition. But it’s essential to achieving broad participation – as demonstrated by the overwhelming number of countries already offering contributions. And without broad participation, no agreement can be effective.

This top-down/bottom-up hybrid draws on the successes and failures of the past two decades, from the Kyoto Protocol to the Cancun Agreements. It establishes a fundamentally new paradigm – and this time I believe we’ve got it right.

A good agreement requires a good process

The French hosts proved that they’d absorbed the hard lessons of the ill-fated Copenhagen conference six years ago, where secret drafts, closed meetings, and other procedural missteps created a poisonous atmosphere of mistrust.

By contrast, the process led by French Foreign Minister Laurent Fabius was a model of diplomacy. His watchwords were “transparency” and “inclusiveness,” and he stuck to them, earning the trust of parties, and building up precious capital that paid off in the final hours.

In exorcising the ghost of Copenhagen, the French helped score a victory for multilateralism generally, and demonstrated that the much-maligned U.N. climate process can in fact deliver.

Governments can’t do it on their own

While it’s up to national governments to deliver – and uphold – the deal, that’s only possible with the help of many, many others.

Never before have so many mayors, governors and CEOs made their presence felt at the international climate talks. They came to Paris to show how they’re stepping up, and to press national governments to do more. Their support gave governments confidence to close the deal, and will help them strengthen their efforts down the road.

But the deal was also made possible by a host of “observer” groups playing public and not-so-public roles. I count C2ES among them. Our Toward 2015 dialogue, which brought together negotiators from two dozen countries for nearly 100 hours of closed-door discussions, help identify many of the “landing zones” for the deal that came together tonight. We’re proud to have played a part.

As many here have said, Paris is not the end, but the beginning. Indeed, many of the details of the new agreement must still be fleshed out.

But the Paris summit has succeeded in capturing the unprecedented political will of the moment and converting it into a solid framework that will keep strengthening our will going forward.