Natural basaltic lava flows occur in many different environments and have a wide range of morphologies that reflect the conditions during flow. Most of the lava on Earth (>60%) is erupted on seafloor along the global mid-ocean ridge system. Eruptions over millions of years, as an integral part of seafloor spreading, have paved the entire seafloor. Submarine eruptions are also important parts of the construction of volcanic island arcs at subduction zones. Despite their importance, active lava flows in these environments have only rarely been directly observed. Older seafloor flows have been widely studied, but the specific conditions that created the range of morphologies seen on the seafloor remain enigmatic. Subaerial lava flows also occur on ocean islands (Hawaii, Iceland, Reunion), continental magmatic arcs (Andes, Cascades) and giant accumulations of flood basalts in Large Igneous Provinces (LIPs, like Columbia River Basalts, Deccan Traps, Siberian Traps) and also have diverse forms. In addition, basaltic lava flows are common elsewhere in our solar system covering large tracts of the terrestrial planets, the Moon and other planetary bodies. Understanding what controls the morphology of lavas in these settings is essential in interpreting volcanic processes across this wide range of environments.