Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 C. Three ternary phases were found: tau1-(Ta,V)5Si3 (Mn5Si3-type), tau2-Ta(Ta,V,Si)2 (MgZn2-type) and tau3-Ta(Ta,V,Si)2 (MgCu2-type). The crystal structure of tau2-Ta(Ta,V,Si)2 was solved by X-ray single crystal diffraction (space group P63/mmc). Atom order in the crystal structures of tau1-(Ta,V)5Si3 (Mn5Si3 type) and tau3-Ta(Ta,V,Si)2 was derived from X-ray powder diffraction data. A large homogeneity range was found for tau1-(TaxV1-x)5Si3 revealing random exchange of Ta and V at a constant Si content. At 1500 C, the end points of the tau1-phase solution (0.082-x-0.624) are in equilibrium with the solutions (Ta1-xVx)5Si3 (Cr5B3 type, 0-x-0.128) and (TaxV1-x)5Si3 (W5Si3 type, 0-x-0.048).