Capacity planning involves determining the production capacity needed by an organization to meet demand. It considers both short-term and long-term managerial planning and control of resources. Key aspects of capacity planning include designing facilities to accommodate large changes in long-term demand, making limited adjustments for seasonal fluctuations using methods like inventory control and adjusting workforce size, and making finer short-term adjustments to meet random demand changes. Effective capacity planning requires evaluating factors like technology, costs, flexibility, and demand uncertainty when selecting optimal plant sizes and production levels.