In this article, the H ∞ filtering problem for switched nonlinear systems under synchronous and asynchronous switching is addressed. First, H ∞ filtering under synchronous switching is investigated; however, the H ∞ filtering performance cannot be guaranteed when there exists asynchronous switching, which is shown in a numerical example in this article. We then consider asynchronous case. At first the totally asynchronous switching is considered, then by the results of synchronous and totally asynchronous case, H ∞ filtering under partially asynchronous switching is derived. Several numerical examples are given to illustrate the effectiveness of the proposed results.