Existing and new applications for the use of multiple hydrocyclone networks are reviewed and discussed. These include the design of multiple product separations, washing-classification circuits and the more efficient classification circuits. The optimal design of hydrocyclone networks is of particular interest since, in principle, it should be possible to target the design to meet given process objectives. In practice this approach is constrained to the design of processes for which adequate models to described hydrocyclone behaviour are readily available. These concepts are explored for treatment of effluents involving siliceous feed materials.