In the article the notion of decompression is defined and explained as distinct from the notion of compression. Decompression in simultaneous interpreting is defined as a result of such formulation of an idea that is longer (expanded) in comparison with the probable compressed version which might be used in the normal conditions of interpretation. The definition suggests that the term “decompression” is more applicable to the operation used in simultaneous interpreting than the term “expansion”. Two categories of decompression are differentiated between: justified decompression and unjustified decompression. Six types of justified decompression are discussed: SDR (speech delivery rate) conditioned decompression, source language conditioned decompression, target language conditioned decompression, source text conditioned decompression, target text conditioned decompression, audience conditioned decompression. The basis for differentiating between the types of decompression is the lingual and extralinguistic factors that influence the process of interpreting.