  Soliton propagation is usually described in the ``slowly varying envelope
approximation'' (SVEA) regime, which is not applicable for ultrashort pulses.
We present theoretical results and numerical simulations for both NLS and
parametric ($\chi^{(2)}$) ultrashort solitons in the ``generalised few-cycle
envelope approximation'' (GFEA) regime, demonstrating their altered
propagation.
