The replica trick computes entanglement entropy via the identity S = −lim_{n→1} ∂_n Tr(ρ^n). By computing Tr(ρ^n) for integer n (the Rényi entropies S_n = log Tr(ρ^n)/(1−n)), one analytically continues to n→1 to recover von Neumann entropy. In 2D CFT, Tr(ρ_A^n) is computed on an n-sheeted Riemann surface, yielding S_n = (c/6)(1+1/n) log(ℓ/ε). The twist operators at the endpoints of region A have conformal dimension h_n = (c/12)(n − 1/n). This same structure appears in holography where the n replicas become n copies of the bulk geometry.