Abstract: This invention concerns affinity tools for oligomeric forms of tau protein. It relates to the field of neurodegeneration, more particularly to the field of tau-related diseases and tauopathy. The invention provides novel tau antibodies and antibody fragments, nucleic acids encoding such antibodies and antibody fragments, cell lines producing such antibodies and antibody fragments, antibody compositions, and kits for the detection of aggregated tau and for the diagnosis of diseases involving aggregated tau. The invention further provides methods for the detection of aggregated tau, for the diagnosis of diseases involving aggregated tau, and for the identification of compositions interfering with the formation and/or stability of tau aggregates.