In this paper, the Wiener–Hopf factorization problem is presented in a unified framework with the Riemann–Hilbert factorization. This allows to establish the exact relationship between the two types of factorization. In particular, in the Wiener–Hopf problem one assumes more regularity than for the Riemann–Hilbert problem. It is shown that Wiener–Hopf factorization can be obtained using Riemann– Hilbert factorization on certain lines.