Zwitterionics (here, alkyldimethylammonium carboxybetaines) are widely used in applications which require "mildness", e g cosmetics and isolation of membrane proteins, although they are known to interact strongly with other charged surfactants. They are interesting because of their unusually high solubility, because their surface behaviour suggests a large conformational change as the spacer length in the head group is increased, and because of a strong asymmetry in their interaction with charges, and presumably with charged surfactants. We propose (a) to study the structural changes associated with the large change in limiting surface tension as a function of head group spacer and (b) to study the interactions with anionic (SDS) and cationic (C12TAB) surfactants with a view to following the asymmetry of the interaction as a function of head group chain length.