Abstract. We characterize t-structures in stable ∞-categories as suitable quasicategorical factorization systems. More precisely we show that a t-structure t on a stable ∞-category C is equivalent to a normal torsion theory F on C, i.e. to a factorization system F = (E, M) where both classes satisfy the 3-for-2 cancellation property, and a certain compatibility with pullbacks/pushouts.