The brachytherapy process requires consistent reference dosimetry that is traceable to metrological primary standards and common procedures to be followed for reference dosimetry globally. The Code of Practice is addressed to both Secondary Standards Dosimetry Laboratories and hospitals. It fulfils the need for a systematic and internationally unified approach to the calibration and use of vented well-type re-entrant ionisation chambers in determining the strength of brachytherapy sources with intensities measurable by such detectors. The dosimetry formalism as well as common procedures for calibration, reference dosimetry, reference-class instrument assessment and commissioning of the well-type ionisation chamber system are provided.