Software architecture is receiving increasing attention as a critical level for software systems. As software architecture design resources (in the form of architectural specifications) are going to be accumulated, the development of techniques and tools to support architectural understanding, testing, reengineering, maintenance, and reuse will become an important issue. This paper introduces a new form of slicing, named architectural slicing, to aid architectural understanding and reuse. In contrast to traditional slicing, architectural slicing is designed to operate on the architectural specification of a software system, rather than the source code of a program. Architectural slicing provides knowledge about the high-level structure of a software system, rather than the low-level implementation details of a program. In order to compute an architectural slice, we present the architecture information flow graph which can be used to represent information flows in a software architecture. Based on the graph, we give a two-phase algorithm to compute an architectural slice.