Mixed micelles of carboxy-terminated surfactants and nonionic surfactants bind to the polycation PDADMAC at a well-defined critical pH corresponding to a critical micelle surface charge density a,. The ionic strength dependence of sigma (c) for this and a number of related polyelectrolyte-micelle systems conforms to the simple result sigma (c) =A kappa (1.4), where kappa is the Debye-Huckel parameter and A varies inversely with polymer linear charge density. The interdependence of sigma (c) and kappa also leads to the observation that binding occurs when the potential due to the micelle exceeds -9 mV at a distance of 8 Angstrom from the micelle surface.