Rényi entropy: Hq = log(Σpᵢq)/(1−q). As q→1: Shannon; q=0: log N (Hartley); q=2: collision entropy; q→∞: min-entropy. Monotone decreasing in q. For uniform dist all Hq equal. For power law distributions, Hq shows rich q-dependence — the "entropy spectrum" reveals multifractal structure.