There is a typical call which I, and I’m sure all other practitioners in the field have been getting from distressed clients all the time. It goes like this: ”Hi, could you please test my air, something feels (smells) wrong”. Or: “I need my air tested to make sure everything is OK.” And it goes on, but I’m sure you see the pattern. Indoor environment quality is probably one of the most illusive-like concepts to general population and for that reason education is very important part of my job. The way I (and most other competent professionals) work when called about a problem is to conduct investigation with the goal of determining the source of the problem, followed by creating a hypothesis which is then tested either by sampling the air for particular parameter/s (contaminant) or by using other necessary tools for the task. Should the hypothesis be confirmed and source of the problem has been discovered, recommendation is made for remediation. I emphasize this again, goal is to remove the source if any way possible, if not, next best thing is to isolate it. Should the hypothesis proved to be wrong, further investigation is taking place and new one is presented and again tested, and so on till you get it right. Investigations could be quite simple as only walk-through and visual inspection paired with the practitioner’s experience may prove to be sufficient, and on the other hand it may turn into a “mission impossible” including multiple air and material sampling methods, building science and air distribution (HVAC) system diagnostics in a multi storey building.