Reference Materials (RMs) and Certified Reference Materials (CRMs) are widely used in all stages of measurement procedures and in interlaboratory comparisons. CRMs, in particular, play a key role in implementing the concept of metrological traceability of measurement results in chemistry, biology and physics among other sciences dealing with substances and materials and, in this context, laboratories use CRMs as readily accessible measurement standards. In the past decades, an extensive production of RMs and CRMs was carried out. Although some of them are intended for applications in physics, the great majority belongs to the amount of substance related fields. There are various normative references dealing with RMs and CRMs, and a broad scientific literature. This work aims at presenting a general overview on the production and characterization of RMs and CRMs, with particular focus on gaseous CRMs. An example of application of gaseous CRMs to support climate change studies is also given.