We study information resonance -- the extra weight people attach to information from people similar to them -- and examine its consequences. In a new lab experiment designed to isolate resonance, we show that people follow the advice of strangers who share characteristics with them at a much higher rate. We find that this is true not only for shared demographics or political identities, but also a broad range of beliefs, personality traits and even superficial preferences and we measure these effects in several types of choices. In the experiment, resonance affects a range of choices, including financial decisions. The structure of our design makes it unlikely that this is a fully rational behavior. To examine the consequences of resonance, we show how to re-purpose a standard information diffusion model, replacing geographic proximity with characteristic similarity. The model explains why role models matter, how social media can erode authority, and why promotion rules that look neutral can still produce homogeneous leadership teams. Finally, field evidence connects micro biases to aggregate outcomes: young workers disproportionately enter occupations already staffed by ethnically similar incumbents, and disproportionately leave those occupations when ethnic elders experience negative labor market shocks. By weaving together micro behavior, theory tools and macro consequences, the paper uncovers new levers for firms and policymakers to manipulate or assist investors.