We review a class of non-topological defects in the standard electroweak
model, and their implications. Starting with the semilocal string, which
provides a counterexample to many well known properties of topological
vortices, we discuss electroweak strings and their stability with and without
external influences such as magnetic fields. Other known properties of
electroweak strings and monopoles are described in some detail and their
potential relevance to future particle accelerator experiments and to baryon
number violating processes is considered. We also review recent progress on the
cosmology of electroweak defects and the connection with superfluid helium,
where some of the effects discussed here could possibly be tested.Comment: 86 pages; submitted to Phys. Re