The purpose of this article is to verify the hypothesis put forward by the author which states that the current methods, including the author’s mechanism, utilized to design the company’s assortment policy can be applied at all stages of assortment management. This article looks at the concept of the company’s assortment policy as a synthesis of traditional and relationship marketing. The author formulates and describes five corporate assortment management stages based on the I.K. Adizes theory of corporate life cycle: primary assortment choice, active assortment expansion, assortment maturity, loss of the assortment relevance, disposal of assortment. The author proposes an organizational and economic mechanism for the introduction of category management in the corporate assortment policy, the category management being focused on the second–fourth stages of corporate assortment management. The mechanism consists of the following elements: a goal, objectives, organizational elements, tools, principles, stages of product category management. The algorithm of product category management, which is a part of the author’s mechanism, is divided into three blocks: development, implementation, and evaluation. Since the scientific literature is known to have many studies devoted to the practices of implementing existing mechanisms at the second–fourth stages of corporate assortment management, the author attempts to introduce the mechanism in a case study of a trading company which is at its first stage of assortment management. The article describes the results of this mechanism implementation. Having obtained the results of the study, the conclusions, and recommendations, the author has finalized the mechanism as a product category management algorithm mainly applied by trading companies at their first stage of assortment management.