Do you know what scalability really is? It's a mathematical function that's simple, precise, and useful. REALLY useful. It describes the relationship between system performance and load. In this talk you'll learn the function (the Universal Scalability Law), how it describes and predicts system behavior you see every day, and how to use it in practice. I'll show you how to understand the function, how to capture the data you need to measure your own system's behavior (you probably already have that), and how to analyze the data with the USL. You'll leave this talk knowing exactly what scalability is and what causes non-linear scaling. There are two factors, and you'll start seeing those everywhere, too. As a result, when systems don't scale you'll know what kind of problem to look for, and you'll avoid building bottlenecks into your systems in the first place. Final note: this talk requires zero mathematical skill.