This chapter presents techniques related to in-market forecasting. The subtleties of trending, however, are much more complex, and selecting the appropriate approach for trending historical data is the key judgement a forecaster makes for in-market forecasting. The overarching principle is to use the historical measures that can be most accurately tracked and that best represent historical market dynamics. Similar to the insights gained from trending multiple datasets relevant to the product, trending market data relative to product data leads to insights on product performance as well as overall market growth. Carryover rates are specific to market conditions, therapeutic areas and product lifecycles. The value of response curve analysis extends beyond forecasting changes in demand. The theory behind promotion response analysis is the same as marketing intervention triangles–quantify the effects of specific marketing interventions and use the results of the analysis to forecasting the effect of interventions.