Solutions containing the potential radiotherapy radionuclide 1 7 7 Lu have been standardized at the National Institute of Standards and Technology (NIST) by 4πβ liquid scintillation (LS) counting with 3 H-standard efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were made with 4π NaI(Tl) γ-ray spectrometry. Activity determinations were made on 4 solutions over the course of 10 months with an expanded (k=2) uncertainty on the activity of 0.8%. Half-life measurements were carried out using the NIST ''4π'' γ ionization chamber (IC) and LS counting and gave a new value of 6.65+/-0.01d, which is shorter than the current ENSDF-recommended value by 1.3%. Impurity analyses were performed by high-purity germanium (HPGe) γ-ray spectrometry and indicated only the presence of 1 7 7 m Lu at a level of 0.02% that of the 1 7 7 Lu as of the respective reference times for the four solutions. Calibration factors for the NIST IC and Vinten 671 ionization chambers were developed, as were dial settings for the NIST-maintained Capintec CRC-12.