To the manager of a firm producing goods or services, quality is the degree to which the product meets specifications. Quality control has become one of the most important precepts of business.

The expression “quality cannot be inspected into a product” is a central theme of organizations today. More and more world-class companies are following the ideas of total quality management (TQM), which emphasizes the entire organization, from supplier to customer.

Statistical aspects of quality control date to the 1920s but are of special interest in our global marketplaces of this new century. Statistical process control tools described in this chapter include the $\overline{x}$- and R-charts for variable sampling and the p- and c-charts for attribute sampling.