  Methods and insights from statistical physics are finding an increasing
variety of applications where one seeks to understand the emergent properties
of a complex interacting system. One such area concerns the dynamics of
language at a variety of levels of description, from the behaviour of
individual agents learning simple artificial languages from each other, up to
changes in the structure of languages shared by large groups of speakers over
historical timescales. In this Colloquium, we survey a hierarchy of scales at
which language and linguistic behaviour can be described, along with the main
progress in understanding that has been made at each of them---much of which
has come from the statistical physics community. We argue that future
developments may arise by linking the different levels of the hierarchy
together in a more coherent fashion, in particular where this allows more
effective use of rich empirical data sets.
