A hyperpycnal flow forms when a land derived dense flow enters a marine or lacustrine water reservoir. As a consequence of its excess in density, the flow plunges in coastal areas generating a highly dynamic and often long lived dense underflow. Depending on the characteristics of the parent flow (flow duration and flow type) and basin salinity the resulting deposits (hyperpycnites) can be very variable. According to flow duration, hyperpycnal flows can be classified into short lived (SLHF) or long lived (LLHF) hyperpycnal flows. SLHF lasts for minutes or hours, and are mostly related to small mountainous river discharges, alluvial fans, collapse of natural dams, landslides, volcanic eruptions, jökulhlaups, etc. LLHF last for days, weeks or even months, and are mostly associated to medium to large size river discharges. Concerning the characteristics of the incoming flow, hyperpycnal flows can be initiated by non-Newtonian (cohesive debris flows), Newtonian supercritical (lahars, hyperconcentrated flows, and concentrated flows) or Newtonian subcritical flows (bedload, sandy or muddy dominated fully turbulent flows). Once plunged, non-Newtonian and Newtonian supercritical flows require steep slopes to accelerate, allow the incorporation of ambient water and develop flow transformations to evolve into a turbidity current and travel farter basinward. Their resulting deposits are difficult to differentiate from those related to intrabasinal turbidites, except for the occurrence of extrabasinal elements like wood, charcoal or plant remnants. On the contrary, Newtonian subcritical hyperpycnal flows (NSHF) are capable of transfer huge volumes of sediment, freshwater and organic matter far from the coast with gentle or flat slopes. In marine settings, the buoyant effect of interstitial freshwater in bedload and sandy hyperpycnal flows can result in lofting due to density reversal. Since the excess of density in muddy hyperpycnal flows is provided by silt-clay sediments in turbulent suspension, lofting is not possible even in marine basins. NSHF can also erode the basin bottom during its travel basinward, allowing the incorporation and transfer of intrabasinal organic matter and sediments. Long lived NSHF deposits exhibit typical characteristics that allow a clear differentiation respect to those related to intrabasinal turbidites. Main features include (1) complex beds with gradual and recurrent changes in sediment grain size and sedimentary structures, (2) mixture of extrabasinal & intrabasinal components, (3) internal and discontinuous erosional surfaces and (4) lofting rhythmites in marine settings.