Research in motion planning has been striving to develop faster and faster planning algorithms in order to be able to address a wider range of applications. In this paper a novel real-time motion planning framework, called decomposition-based motion planning, is proposed. It is particularly well suited for planning problems that arise in service and field robotics. It decomposes the original planning problem into simpler subproblems, whose successive solution results in a large reduction of the overall complexity. A particular implementation of decomposition-based planning is proposed. It is based on an adaptive wavefront expansion algorithm and reactive motion execution. Using this implementation of decomposition-based planning, real-time motion planning performance for an eleven degree-of-freedom mobile manipulator can be achieved. Some fundamental and preliminary analysis of the decomposition-based motion planning approach is provided.