Sampling and analysis of materials in the gas phase is not covered in general sampling standards and guides, due to the complex nature of the subject matter. Most gas-phase materials exist in the region from ambient temperatures (~300 K) to combustion temperatures typically around ~1200 K. Common to both temperature range margins, though predominantly for hot gases, is the fact that continuous reactions often take place in material that is moving at high speeds, presenting less than trivial challenges to conventional Theory of Sampling (TOS). The purposes of representative gas sampling are many, but three standard cases are presented, covering the most dominating scenarios met with in science, technology and industry.