Basic Ideas.- How Cyclones Work.- Cyclone Flow Pattern and Pressure Drop.- Cyclone Separation Efficiency.- The Muschelknautz Method of Modeling.- Computational Fluid Dynamics.- Dimensional Analysis and Scaling Rules.- Other Factors Influencing Performance.- Measurement Techniques.- Underflow Configurations and Considerations.- Some Special Topics.- Demisting Cyclones.- Foam-Breaking Cyclones.- Design Aspects.- Multicyclone Arrangements.