What are ‘rationality meetups’?

The rationality community first sprang up around the blogs Overcoming Bias and LessWrong around 2007. ‘Meetups’ is the general term we use to refer to in-person rationality communities. As of 2025, there are active communities in about 50 cities around the world, and occasional meetups in nearly 200.

While groups vary in their focus and interests, the rationality community has historically had a focus on truth and reasoning. Many in the community agree that the human mind is prone to predictable mistakes and cognitive biases that we hope to avoid. At their best, members strive to have accurate beliefs about the world and to be able to make effective actions towards their goals.

Rationality meetups use a variety of different names, including ‘ACX meetups’. ACX, or Astral Codex Ten, is a blog written by Scott Alexander, a psychiatrist. Much of Scott’s following found him via his previous blog, SlateStarCodex (SSC), which was active from February 2012 through June 2020, or via his earlier writings on LessWrong and LiveJournal. Many meetups also use the LessWrong brand, which is owned by Lightcone Infrastructure.