Pulsars are potentially the most remarkable physical laboratories we will
ever use. Although in many senses they are extremely clean systems there are a
large number of instabilities and variabilities seen in the emission and
rotation of pulsars. These need to be recognised in order to both fully
understand the nature of pulsars, and to enable their use as precision tools
for astrophysical investigations. Here I describe these effects, discuss the
wide range of timescales involved, and consider the implications for precision
pulsar timing.Comment: Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and
Opportunities after 80 years", J. van Leeuwen (ed.); 6 pages, 0 figures, 2
table