Topological defects formed at symmetry-breaking phase transitions play an important role in many different fields of physics. They appear in many condensed matter systems at low temperature, including vortices in superfluid He-4, defects in He-3, quantized magnetic flux tubes in type-II superconductors, and disclination lines and other defects in liquid crystals. In cosmology, unified gauge theories of particle interactions suggest a sequence of phase transitions in the very early universe, some of which may lead to defect formation. In astrophysics, defects play an important role in the dynamics of neutron stars. The present book begins with a Condensed Matter - High Energy & Cosmology dictionary, prepared by Grigory Volovik, which gives a common basis to ideas pertaining to these branches of modern physics. The following papers, written by experts in their respective fields, provide the fundamental concepts of symmetry-breaking phase transitions. The book represents the fruits of an exchange of ideas between particle physicists, cosmologists and condensed matter physicists.