Superconductivity, once considered the most completely understood many-body problem in physics, continues to provide physicists with a profound intellectual challenge. Studying the behaviour of such diverse materials, from heavy fermion to organic to the high-profile copper-oxide superconductors, has ultimately lead to the re-evaluation of one of the cornerstones of condensed matter physics, namely Fermi liquid theory.
Throughout the development of this field, thermal conductivity measurements have continued to provide some of the least ambiguous experimental results. I will demonstrate, not only how such measurements can help classify the unconventional nature of the superconducting state, but crucially the underlying normal state as well. Of fundamental interest are the results in the normal state of the high-$T_c$ cuprates, which are sufficiently far-reaching as to question the integrity of the electron itself.