**1. Introduction**

Electromagnetic fields, in particular so-called radiofrequencies are used by mobile or wireless communication systems as for example GSM mobile telephones, DECT telephones, wifi etc. Recent years were characterized by a tremendous increase in applications and types of wireless communication systems and this is responsible for an important increase in human exposure to radiofrequency radiation. Discussions on alleged adverse health effects are going on for years and so far no consensus agreement has been reached. These discussions are held amongst scientists as well as amongst laymen from the general public and authorities. Radio, TV, newspapers and magazines often bring erroneous information to the public. But also scientists do not agree. The scientific literature is full of papers showing that these fields can be dangerous and others showing that they are not. This holds true for virtually all possible endpoints and scientific disciplines that were studied, going from *in vitro* studies on cell proliferation, genetic and immunological effects, over animal experimental data on cancer and non cancer issues and human epidemiological investigations. It is not uncommon that controversial results are reported by the same laboratory. This results in claims of 'danger' when reference is made to essentially 'positive' papers (showing adverse biological effects) or claims of innocuity when only papers showing no effects are emphasized. It is clear that all (peer reviewed) scientific data should be considered and carefully analysed in order to come to a best possible 'weight of evidence' evaluation of risk. According to the WHO (World health Organisation) and ICNIRP (International Committee on Non Ionizing Radiation Protection) a single study does not provide the basis for hazard identification. It can at the best form the basis of a hypothesis. Confirmation of the results of any study is needed through replication and/or supportive studies. Only the resulting body of evidence forms the basis for science-based judgments by defining exposure levels for adverse health effects and no observable adverse effects.

This is recognized by most scientists all over the world and this explains why there were and still are many expert groups issued from the scientific community that evaluate(d) the alleged adverse health effects of radiofrequency fields in general, and mobile telephone frequencies in particular. It should be noted that radiofrequencies pose the additional problem (not encountered with other agents) that effects can be thermal or non thermal. At high exposure levels cells or tissues can heat and thermal effects can be observed that are not obtained by normal environmental exposure levels as for example. when exposure is to radiation from a mobile phone base station antenna or when using the handset. Thermal effects are well known but experiments where thermal exposure levels were studied are not relevant in the discussion of "mobile phones and health". Yet, often thermal exposure levels were used, even when the authors of the study claimed that they investigated non thermal exposure levels (wrong experimental set up and dosimetry). It is therefore also important to evaluate not only the biology but also the dosimetric aspects of an investigation.

The purpose of the present chapter is to give an overview of the conclusions of different (inter)national expert groups based on their analyses.
