Proposed in this letter is the concept of impedance strengthening and weakening (ISW) networks, which can be used to describe the working mechanism of power converters and lead to a generalized impedance-based design principle. Impedance strengthening in a converter refers to the load impedance being higher than the input equivalent impedance, leading to voltage gain. Conversely, impedance weakening results in voltage reduction. In this study, the idea of ISW networks is applied for understanding existing converters, and a novel converter design method is then proposed. Experiments are conducted on a few new converter topologies to demonstrate the application of the proposed ISW concept.