This thesis explores the influence that meltwater exerts on styles of ice-marginal sedimentation, using past and present examples from Iceland. The study glaciers display marked contrasts in form, size and composition of moraines which are unlikely to reflect differences in rates of subglacial erosion. This is because the study glaciers occupy a similar climate, show similar relief, sit above similar bedrock, and are inferred to flow at similar speeds. The observed variation in moraine properties must reflect some other process which intervenes to modify sediment transport relationships prior to the arrival of debris at the ice edge. I argue that this key factor which controls sediment transport - and, as a result, the potential to form moraines - is the behaviour of subglacial meltwater flows. Studies of the sediment load of its outlet river show that Sólheimajökull is a highly erosive glacier, yet the quantity of debris carried by the ice is extremely small. Consequently, present-day moraine formation is extremely limited. This can best be explained as the product of an aggressive subglacial drainage network which captures and evacuates the bulk of debris generated by subglacial erosion. This state of high efficiency subglacial flushing is likely to dominate the sediment budget of many temperate glaciers. Whereas the present-day margin of Sólheimajökull is debris-poor, the present-day margins of Gígjökull and Steinholtsjökull are debris-rich. This debris consists of two major populations: 1) rounded closets set in a sorted coarse sand and gravel matrix, derived from a series of englacial debris bands, and 2) sub-angular clasts in a poorly-sorted matrix, derived from unusually thick sequences of basal ice.