Despite a certain simplicity and a well-defined methodology for the assessment of odour emissions from point sources and active area sources, odour sampling on passive area sources is still a rather debated task, meaning that, up to now, there is not a codified sampling procedure allowing to give reproducible results among different laboratories. Three different kinds of area sources can be distinguished, i.e. liquid passive area sources, solid passive area sources, and landfill surfaces. These three different types of sources are characterized by different volatilization and/or emission phenomena, and shall thus be treated differently while sampling in order to assess a representative odour emission rate. This paper aims to give an up-to-date overview of the principles and methods for odour sampling on passive (or semi-passive) area sources as well as for the estimation of the odour emission rates relevant to those sources, most of which still require further development and validation. The considerations here proposed highlight how the understanding of the volatilization phenomena that constitute the odour emission are fundamental for the evaluation and quantification of odour emissions.