  The recent results (Pardo & Poretti 1997, A&A 324, 121; Poretti & Pardo 1997,
A&A 324, 133) obtained on the frequency content of Double-Mode Cepheids light
curves and the properties of their Fourier parameters are reviewed. Some points
briefly discussed in previous papers (no third periodicity, methodological
aspects on the true peaks detection, the action of the cross coupling terms and
the impact on theoretical models) are described.
