  In this article we review the effects of magnetic frustation in the stacked
triangular lattice. Frustration increases the degeneracy of the ground state,
giving rise to different physics. In particular it leads to unique phase
diagrams with multicritical points and novel critical phenomena. We describe
the confrontation of theory and experiment for a number of systems with
differing magnetic Hamiltonians; Heisenberg, Heisenberg with easy-axis
anisotropy, Heisenberg with easy-plane anisotropy, Ising and singlet ground
state. Interestingly each leads to different magnetic properties and phase
diagrams. We also describe the effects of ferromagnetic, rather than
antiferromagnetic, stacking and of small distortions of the triangular lattice.
