  We begin this review with an introduction and a discussion of Weyl fermions
as emergent particles in condensed matter systems, and explain how high energy
phenomena like the chiral anomaly can be seen in low energy experiments. We
then explain the current interest in the field due to the recent discovery of
real materials which behave like Weyl semi-metals. We then describe a simple
lattice model of a topological insulator, which can be turned into a Weyl
semi-metal on breaking either time-reversal or inversion symmetry, and show how
flat bands or Fermi arcs develop. Finally, we describe some new phenomena which
occur due to the chiral nature of the Weyl nodes and end with possible future
prospects in the field, both in theory and experiment.
