Liquid-infused surfaces (or lubricant-infused surfaces) (LIS) are a new class of functional materials
introduced in 2011. Their exceptional properties have earned them a place at the forefront of many fields
including anti-biofouling, anti-icing, anti-corrosion, drag reduction, droplet manipulation and drop-wise
condensation. Integral to their success is the infused lubricant layer which affords them their properties. In
this review, we examine the current state of the literature relating to the lubricant layer. We consider the
lubricant through all stages in the surface’s lifecycle from design, to use, all the way through to depletion
and eventual failure. First, we examine trends in lubricant choice and how to choose a lubricant, including
environmental and medical considerations. We then look at the different methods used to infuse lubricant
into surfaces and how lubricant depletes from the surface. We then report direct and indirect methods to
characterise the thickness and distribution of the lubricant layer. Finally, we examine how droplets interact
with LIS and the unique properties afforded by the lubricant before providing an outlook into where
research centred on understanding the lubricant layer is heading in the new decade