The objective of auxiliary ventilation in underground mines is to deliver sufficient air quantity and quality to all workplaces through the use of combination of fans, ducts and airflow controls. This 256-page updated manual is intended to provide an overview of auxiliary ventilation and to present guidelines for the design and effective operation and management of auxiliary ventilation systems. The manual features new chapters on dilution ventilation and ventilation economics, a new appendix with case examples. It is restricted mainly to underground hard rock mine operations.