Assortment planning is the process conducted by the retailer to determine the number and options (style-color) in a line. Key questions that arise in this process include choosing the inventory depth and variety breadth, and the mix between basic and fashion merchandise of the assortment to maximize expected profits.

It is crucial that retailers manage this process efficiently as poor assortment planning leads to markdown costs due to excessive inventory of unpopular products and lost sales opportunities due to rapid sellouts of popular products.

Assortment planning is how fashion retailers plan their assortment of seasonal styles and allot them to each store and other sales channels. The idea is to offer the right styles, in the right colors, through the right channels