  This article provides an overview of stellar instabilities as sources of
gravitational waves. The aim is to put recent work on secular and dynamical
instabilities in compact stars in context, and to summarize the current
thinking about the detectability of gravitational waves from various scenarios.
As a new generation of kilometer length interferometric detectors are now
coming online this is a highly topical theme. The review is motivated by two
key questions for future gravitational-wave astronomy: Are the gravitational
waves from various instabilities detectable? If so, what can these
gravitational-wave signals teach us about neutron star physics? Even though we
may not have clear answers to these questions, recent studies of the dynamical
bar-mode instability and the secular r-mode instability have provided new
insights into many of the difficult issues involved in modelling unstable stars
as gravitational-wave sources.
