Describes how lumber can be dried most effectively under outdoor conditions, and illustrates air-drying principles and procedures developed through field investigations and observations of industrial practices. Particular emphasis is placed on the yarding of lumber in unit packages. Included are such subjects as why lumber is dried, advantages and limitations of the process, properties of wood in relation to drying, the drying yard layout, piling methods, causes and remedies of air-drying defects, factors affecting the cost of air drying, and protection of air-dried stock.