Mercury is a complex, multifaceted contaminant which can take many different forms. It is poisonous to humans and wildlife and damaging to the environment. Currently, around two thirds of the mercury entering the environment comes from current or legacy human sources including mining, industrial activities, coal combustion and incinerators, with the remaining originating from natural sources. A special issue addressing the most up-to-date science on the fate and effects of mercury has now been published in Springer’s journal Ambio.