Due to the resource constraints of the factors of production (land, capital, capacity, etc.), the firms have to rationalize the assortment of products that they deal in. In such a situation, a consumer whose requirement for a preferred product may not get served from the existing inventories with the seller, may go for some other alternative product. A lot of research work in the past has been done on this demand substitution and its implications upon the assortment optimization, inventory optimization and price optimization. The first work on modelling for substitutable demand is attributed to 1970. Considering the same, the authors decided to do a review of the half-century of work on the modelling for substitutable products. The paper gives a detailed analysis of the published research articles around demand substitution and also discusses the achievements of the existing research. The article also gives a few possibilities of the future extensions to this body of knowledge on the management of substitutable products.