A viral loop exists when using a product naturally exposes new potential users to it, creating an exponential growth engine. This article deconstructs the mechanics of viral loops: the viral coefficient (K-factor), cycle time, and the conditions under which virality can be sustained. It categorizes viral loops into types — inherent (Zoom), collaborative (Google Docs), incentivized (Dropbox), and social (Instagram) — and provides practical guidance on designing viral mechanics into products. The article cautions against artificial virality and emphasizes that genuine product value must underpin any viral strategy.