We report a new colloidal synthesis of niobium-doped TiO2 anatase nanocrystals (NCs) that allows for the prepn. of ∼10 nm NCs with control over the amt. of Nb doping up to ∼14%. The incorporation of niobium ions leads to the appearance of a tunable, broad absorption peak that ranges from the visible range to the mid-IR. This optical behavior is attributed to the substitution of Nb5+ on Ti4+ sites generating free carriers inside the conduction band of the TiO2 NCs as supported by optical and ESR spectroscopic investigations. At the same time, the incorporation of progressively more niobium ions drives an evolution of the shape of the NCs from tetragonal platelets to "peanutlike" rods.