This document outlines Trello's process of developing product principles to guide design decisions. It began with informal "Trello-y" guidelines that caused confusion. Formal principles were introduced to be universal, easy to understand, describe how not what, and complement quantitative data. The principles are visual, direct, flexible, collaborative, fun, succinct, and personal. They are demonstrated through improved onboarding that is more visual, direct, and performs better. The principles provide a framework to critique designs and make decisions while still allowing flexibility.