Aggregate planning involves intermediate-range planning from 2-18 months to determine overall levels of output, employment, and inventory. It aims to balance demand and capacity over time. The key steps are to forecast aggregate demand, set output, employment, and inventory targets, and periodically update the rolling plan. Demand and capacity options like pricing, promotions, overtime/slack time, inventory, and subcontracting can be used to better match fluctuations. The optimal plan is selected by developing alternatives and choosing the lowest cost option that meets objectives.