of complexes between antibodies and either the ectodomain (sE) of the viral E protein or its domain 3 (ED3) have helped understand the molecular bases of the virus recognition and neutralization. Some of the epitopes are partially or totally inaccessible in the known structure of the mature virion. The corresponding antibodies are, therefore, assumed to bind to alternate or transitional conformations of the virus at 37 °C. The murine antibody E111 neutralizes DENV1. Its Fab and scFv fragments were crystallized in complex with the ED3 domain of DENV1. Its epitope is located around β-strands C and C' of ED3, and the intervening loop. The murine antibody 1A1D-2 strongly neutralizes DENV1, DENV2, and DENV3. Its Fab fragment was crystallized in complex with the ED3 domain of DENV2. Its epitope straddles β-strands A and G of ED3. The murine antibody 2H12 cross-reacts with all four DENV serotypes. It neutralizes the corresponding viruses, except DENV2. Its Fab fragment was crystallized in complex with the ED3 domains of DENV1, DENV3 and DENV4. Its epitope is located around the conserved AB loop of ED3. The murine antibody 4E11 neutralizes all four DENV serotypes with varying efficacies. Its scFv fragment was crystallized in complex with the ED3 domains of the four DENV serotypes. Its epitope straddles β-strands A and G of ED3 as does the epitope of 1A1D-2. The structures at 2.0 Å resolution have enabled one to analyze the roles of water molecules within the protein interfaces and the roles of somatic hypermutations outside of these interfaces in the interactions and cross-recognitions. The chimpanzee antibody 5H2 potently neutralizes DENV4. Its Fab fragment was crystallized in complex with the sE protein of DENV4. Its epitope is included in domain 1 (ED1) of the E protein. The human antibodies Ede1-C10, Ede2-A11, and Ede2-B7 potently neutralize all four DENV serotypes. Their Fab or scFv fragments were crystallized in complex with the sE protein of DENV2. The recognition determinants of these antibodies are at a serotype-invariant site in the E dimer interface and include the exposed side chains of the E fusion loop and the two conserved glycan side-chains. Disease Common names for dengue fever include breakbone fever, vomiting and dandy fever; dengue hemorrhagic fever and dengue shock syndrome are the severe forms. Dengue is found in tropical and subtropical climates worldwide, mostly in urban and semiurban areas. People of all ages who are exposed to infected mosquitoes are