One of the major challenges in variety management of modular product families is to prevent continuously generated variants of design elements. This paper aims to provide guidance on how manufacturing companies can reduce a large number of variants that have already increased from the existing product architectures. This paper introduces a new concept of architecture named variation architecture ( VA) in which relationships between variants in the market, design, and production domains are arranged explicitly for planning variety of a modular product family. Since the VA includes two perspectives which are domain mapping and variant-level planning, it can help companies to systematically establish complex relationships between variants across the domains. This paper describes elements of the three domains, relationship types between elements, and four categories of relationship rules called management rules at the variant-level planning. A framework is proposed for reducing variants through the VA to demonstrate its applicability. In the case study, we apply the framework to a front chassis family having a large number of variants and show that the VA significantly reduces unnecessary variants compared to the currently being produced.