A unital ring is called clean (resp. strongly clean) if every element can be written as the sum of an invertible element and an idempotent (resp. an invertible element and an idempotent that commutes). Prof. T. Y. Lam proposed a question: which von Neumann algebras are clean as rings? In this talk, we will give the answer about Lam’s question and show that all finite von Neumann algebras are clean and all separable infinite factors are clean. We also show that a von Neumann algebra is strongly clean if and only if it is a finite direct sum of finite type I von Neumann algebras.