Binary mixtures of a poly(ethylene oxide-block-2-(diethylamino)ethyl methacrylate) (PEO-PDEA) copolymer and poly(methacrylic acid) (PMAA) can form three types of micelles/aggregates in aqueous solution at ambient temperature, depending solely on the solution pH. Above pH 8.5, simple micelles are formed with hydrophobic PDEA cores and with the PEO chains located in the corona; the PMAA does not participate in micelle formation under these conditions. However, at pH 6-8.5, polyion complex micelles with charge-compensated PDEA/PMAA cores and PEO coronas are obtained. A third colloidal structure is formed below pH 3 due to hydrogen bonding between the PEO and PMAA chains. This remarkable reversible self-assembly behavior is unprecedented.