Contaminants of emerging concern or, simply, emerging contaminants represent a newly discovered group of chemicals present in surface and groundwater. It was only the improvements in analytical instrumentation that allowed for the detection of these contaminants even at trace levels. The continuous detection of new chemicals with time raises questions concerning their source pathways, their fate, transport, transformations and impact on aquatic environments. The scope of this chapter is to present an overview of the contaminants classified as “emerging”, their sources and introduction pathways to the environment and the related risks to human health and aquatic life.