Steeply inclined settlers (SIS) are solid-liquid separators that feature close, inclined confining elements that allow significant settling enhancement when compared to vertical tanks, resulting in relatively low footprints at equal throughput. The present article reviews the working principle, flow configuration, capacity, and several technological advances related to this kind of equipment. The consistency of the Ponder, Nakamura and Kuroda theory, developed after the discovery of the Boycott effect in 1920, which is essential to the settling enhancement effect, and the engineering approach developed independently for the design of SIS settlers during the late 1960's, based on particle trajectory analysis, is established. A discussion about potential developments for future improvement of the technology is made, with emphasis on three main topical areas: improvements of settling element array, optimization of inlet conditions, and potential improvements of the design of settling elements. The application of the technology to the mining industry is discussed in the context of increasing water scarcity and the progressive ore grade decrease.