Much of the rain that falls in monsoon climates is delivered by transient, propagating vortices that are neither typhoons nor classic extratropical baroclinic waves, but another type of synoptic-scale disturbance. This is particularly true in the South Asian monsoon, where monsoon depressions produce extreme rainfall that is responsible for the majority of that region's hydrometeorological disasters. In this presentation we review recent progress in understanding the mechanisms of genesis and amplification of monsoon depressions, including theories for barotropic instability of the low-level monsoon westerlies and for instabilities produced by convective coupling with the background, seasonal mean poleward gradient in water vapor. We discuss historical trends in the frequency, location, and rain rates of monsoon depressions and high-resolution global climate model projections of their future changes. Finally, we close by presenting new operational predictions of monsoon depression activity based on numerical weather prediction model output.