This publication discusses calibration techniques of the most commonly used gamma and beta ray brachytherapy sources. For Cs-137 low dose rate (LDR) source calibrations, the IAEA Dosimetry Laboratory maintains reference sources calibrated at a primary standards dosimetry laboratory. These sources can be used to calibrate well type ionization chambers maintained at the secondary standards dosimetry laboratories. In Section 7 of this report Cs-137 LDR calibrations are discussed in detail.