Forecasting seasonal products can be difficult when the products are fairly new or highly variable. The Spring 2007 issue of Foresight contained a special feature on modeling seasonality in short time series. The articles addressed the issues of minimum sample size requirements and surveyed the options for applying the seasonal patterns that are in aggregates (e.g. product group) as well as in analogous product data to the individual product at hand. Now, Maryam, John, and Aris show specifically how to form product-group seasonal indexes and explain how to determine when group indexes will be superior to individual indexes for forecasting the individual products. They also make the important point that there may be better ways to form product groups for seasonal forecasting than a company’s standard product groupings. Copyright International Institute of Forecasters, 2012