Spaced repetition is the most evidence-backed learning technique available — and the one most systematically ignored. The Cepeda et al. (2006) meta-analysis of 317 experiments confirms it outperforms massed practice across all conditions. But the mechanism most people miss is that the benefit comes from the retrieval attempt, not the re-exposure. This guide covers the neuroscience, the correct Anki implementation, the 85% accuracy calibration rule, the sleep integration that multiplies retention gains, and the cholinergic supplement stack that supports memory encoding.