Zero trust has become one of the most widely referenced concepts in enterprise security, and also one of the most loosely defined in casual conversation. Stripped of marketing language, zero trust rests on a fairly simple principle: never trust a connection by default, verify it explicitly every time, regardless of whether it originates inside or outside the traditional network perimeter. Certificates are one of the most concrete, practical tools for making that principle actually enforceable rather than aspirational. This article covers exactly how the two fit together.