The study of the presence of the various types of bioaerosol in the atmosphere should be backed up by a deep knowledge of the features of the sources from which they are generated: terrestial and aquatic, natural and anthropogenic. The first step needed to work out aerobiological models is the precise description of the location, seasonality, timing and release flow of the particles produced. One of the greatest problems encountered in aerobiology lies in the precise assessment of the airborne particle concentration. The difficulty varies with the kind of particle to be recorded and strongly depends on the method and system utilised. Many aspects in the monitoring of indoor and outdoor bioaerosol have still to be thoroughly investigated. More functional and accurate methods, morphological, chemical, microbiological and inmunological analyses are actual requirements in the fields of atmosphere microbiology, allergenic aerosol and phytopathology. Bioaerosol monitoring is carried out for three principal reasons. Firstly, for general scientific interest and research. Secondly, to meet legal requirements or to comply with guidelines which often state that air quality may have to be monitored but do not specify methodology and thirdly to collect epidemiological data. Physicists expert at aerosol sampling are frequently involved in the research and investigation of proper sampling systems for non viable particles, whereas physicists and biologists should be necessarily involved together in the monitoring of viable bioaerosol. The stress undergone by viable particles during sampling procedures causes steadily an increased death rate of the sampled organisms due to thermal, mechanical chock or dehydratation of the particles. The need for further information on biological aerosol or bioaerosol, is brought about by the availability of approximate data only or worse, by the total lack of the data in papers dealing overall with atmospheric particles. Even keeping into account the difficulty to be overcome when carrying out this kind of measurements, researchers should follow this path further.