As argued in Chapter 1, articulation is the slowest and most energy-consuming stage in human communication. The speaker can spare effort and time by omitting or shortening the forms that represent accessible information – that is, the information already available to the addressee, or easily inferable from the context and general knowledge. In contrast, more effort can be spent on information that is less accessible. We speak of an efficient length asymmetry when there is a negative correlation between formal length and accessibility of information. The chapter discusses diverse formal asymmetries that display this correlation – in lexicon, phonology, morphosyntax and discourse. Alternative explanations are also discussed.