The radiation dose delivered to patients undergoing specific medical x-ray examinations might vary among practices due to the difference in energy, filtration, and technique used to acquire images. In order to minimize this variation, the Diagnostic Reference Level (DRL) was introduced by ICRP in 1996 in publication no.73 as a standard reference dose in medical imaging practice. DRL can be used to promote an optimum range of doses to acquire diagnostic images for specified procedures. The implementation of DRL will be effective only if dose monitoring is regularly conducted, and corrective actions are performed if the doses consistently exceed DRL values. While many studies on DRLs have been published, the concept of DRLs and its implementation might not be familiar to all medical radiation professionals, especially for those who do not have national standard. Therefore, this article is expected to give comprehensive and useful guidelines for medical radiation practitioners regarding DRL in order to promote the establishment and effective implementation of DRL. This article will explore the current literature related to the definition of DRL, steps in establishing DRL, various studies on DRLs, and DRL in paediatric.