We write 3.6 trillion words online -- every single day. How is this explosion of online expression changing the way we think? In this talk, based on my book "Smarter Than You Think: How Technology is Changing Our Minds for the Better", I describe the value of "public thinking" and the science behind it. I'll look at how our everyday acts of communication -- each tweet, each text, each post in an Instagram thread -- shapes our cognition, triggers the "audience effect", and connects ideas together. Thinking in public helps us crystalize our thoughts and collectively tackle problems to big for each of us alone; in my talk, I'll explain how.