From Middle High German *kennen*, Old High German *kennan* ("to make known, recognize"), related to Old English *cennan* ("to declare, make known"). Both derive from Proto-Germanic *kannijaną*, a causative form of *kunnaną* ("to know how"), which also gives English *can* and German *können*. The root traces back to Proto-Indo-European *ǵneh₃-* ("to know"), the same root as Latin *gnoscere/noscere* and Greek *gignōskein*.

German makes a crucial distinction that English does not: *kennen* means to know through acquaintance or experience (people, places, things), while *wissen* means to know a fact. English speakers often mix these up. "Kennst du Maria?" = "Do you know Maria?" (personally). "Weißt du, wie sie heißt?" = "Do you know what her name is?" (a fact). Getting this right is one of the earliest — and most rewarding — milestones for German learners.