The phase behavior of dodecylammonium chloride (DDACI) and L-carrageenan (IC) aqueous mixtures was examined at 298 K by a variety of techniques. The complex interactions between DDACI and IC starting at a very low concentration are accompanied by the formation of a variety of single or coexisting phases, differently structured soluble polyelectrolyte-surfactant monomer complexes, surfactant micelles, polyelectrolyte-micelle complexes, and solid crystalline and gel phases. The multistep mechanism of DDACI and IC interactions is discussed in terms of successive electrostatic, hydrophobic, and intra- and interpolymer interactions.