The present invention concerns methods and compositions for stably tethered structures of defined compositions with multiple functionalities and/or binding specificities. Particular embodiments concern stably tethered structures comprising a homodimer of a first monomer, comprising a dimerization and docking domain attached to a first precursor, and a second monomer comprising an anchoring domain attached to a second precursor. The first and second precursors may be virtually any molecule or structure, such as antibodies, antibody fragments, antibody analogs or mimetics, aptamers, binding peptides, fragments of binding proteins, known ligands for proteins or other molecules, enzymes, detectable labels or tags, therapeutic agents, toxins, pharmaceuticals, cytokines, interleukins, interferons, radioisotopes, proteins, peptides, peptide mimetics, polynucleotides, RNAi, oligosaccharides, natural or synthetic polymeric substances, nanoparticles, quantum dots, organic or inorganic compounds, etc. The disclosed methods and compositions provide a simple, easy to purify way to obtain any binary compound attached to any monomeric compound, or any trinary compound.