The aim of this review is to provide a comprehensive and state-of- the-art review of existing literatures on the enhanced-separation hy- drocyclone technologies developed by optimizing operating parameters and conditions. To achieve a better understanding of these technolo- gies, the enhanced-separation technologies are categorized into two main groups (Fig. 2): (i) operating parameters, including feed flow rate, feed pressure, feed density difference, feed particle parameters (concentration, size, shape, and arrangement), and feed fluid para- meters (viscosity and rheology); and (ii) operating conditions, including electrical hydrocyclones, magnetic hydrocyclones (electromagnetic field and permanent magnetic field), magnetic fluids hydrocyclones, electrochemical hydrocyclones, flocculant-assisted hydrocyclones, hy- drocyclones enhanced by flotation, hydrocyclones enhanced by control particles; hydrocyclones enhanced by adjusting back pressure, and hydrocyclones enhanced by monitoring and automatic control. Both of them are analyzed and summarized according to the critical separation- performance parameters, such as separation efficiency, cut size, split ratio (i.e., the volumetric ratio of underflow to feed flow), energy consumption (usually expressed by the pressure drop of the fluid pas- sing through the hydrocyclone), capacity, and separation sharpness. It is hoped that both the reviewed contents and the proposed challenges may be helpful to the researchers working in this field, and eventually yield some perspective knowledge, which results in the improvement of economic feasibility of separation by hydrocyclones and the expansion of the application scope of hydrocyclones (Fig. 2).