It is now well admitted that most quaternary III–V compounds show unstable regions in the temperature range commonly used in epitaxy. For instance, according to these authors, the InGaAsP alloy, lattice matched to InP and with emitting wavelength 1.3 μm should be unstable at temperatures below 700 °C. Liquid phase epitaxy, however, is commonly performed down to 600 °C. As this growth technique occurs close to thermodynamical equilibrium, such growth should not take place. It was clearly demonstrated that the substrate stabilizing effect is responsible for this paradoxical behavior. Another LPE substrate effect pointed out by Stringfellow is known as the ‘‘pulling effect.’’ Results will be presented showing the connection between these effects in the system InGaAsP/InP and particularly InGaAs/InP. ‘‘Stabilized’’ GaAsSb was also successfully epitaxially grown on InP, in the immiscibility region, from the liquid phase. Microscopic compositional periodical modulations are observed in standard InGaAsP epilayers, if growths are performed below a critical temperature. This phenomena, also related to solid instability, can be interpreted in terms of liquid–solid interfacial spinodal decomposition.