  I review the theory of preheating after inflation, focusing on the recently
found tachyonic preheating in the theories with spontaneous symmetry breaking.
This occurs due to the tachyonic instability of the scalar field near the top
of its effective potential. Contrary to the common expectation, tachyonic
instability converts most of the energy into that of colliding classical waves
very rapidly, within a single oscillation. Efficient tachyonic preheating is
typical for the hybrid inflationary scenario, including SUSY motivated and
brane inflation models.
