In this theoretical background chapter, intensifiers are defined as degree-indicating devices and distinguished from items indicating similar and partly overlapping concepts such as quantification, emphasis, focus, and modality. They are subclassified into the categories of amplifiers (maximizers, boosters) and downtoners (moderators, diminishers, minimizers), with different semantic characteristics and effects. Formally, they are restricted to one-word adverbs, both with and without the -ly suffix. Their typical collocational associations and syntactic behaviour regarding preferred modified targets is dealt with. Their pragmatic distributions in different situational contexts is briefly touched on