Facebook is inherently viral. There are lots of sites that include a contact importer, and for lots of them it doesn't really make sense. For Facebook it fits so well. It wasn't until a few years in that we started building some tools that made it easier to import friends to the site. That was a huge thing that spiked growth.

If Facebook were a country, it would be the 8th most populated in the world, just ahead of Japan.

In a lot of ways Berlin is a symbol for me of Facebook's mission: bringing people together, connecting people and breaking down boundaries.

In a recent survive of Millennials around the world asking what most defines our identity, the most popular wasn't nationality, ethnicity or religion. It was "citizen of the world." That's a big deal. Every generation expands the circle of people we consider one of us. And in our generation, that now includes the whole world. This is the struggle of our time. The forces of freedom, openness, and global community against the forces of authoritarianism, isolationism, and nationalism - forces for the flow of knowledge, trade, and immigration, against those who would slow them down.

It's tough to say, exactly, what things will look like in three to five years, but there's a lot of work to do in just moving along the path that we've already set out.

Betting completely on HTML5 is one of the, if not THE biggest strategic mistake we've made.

Of course the Silicon Valley is unique and Berlin is not yet comparable. But of all the different cities that are building a startup infrastructure, Berlin is the one with the most similar energy.