This Technical Report describes exposure evaluation concepts and techniques for the overall exposure level in spatial regions and occupants caused by the simultaneous exposure to multiple narrowband electromagnetic (EM) sources. Throughout this Technical Report, it is assumed that the exposure evaluation occurs under static conditions, i.e., the source position and transmit-mode characteristics (e.g. emitted power, modulation scheme, etc.) of the device(s) under test do not vary significantly over the time required to carry out the evaluation using the chosen evaluation technique (e.g., field measurements). The vast majority of wireless communication systems worldwide employ signalling schemes featuring narrowband waveforms, hereinafter defined as signal waveforms occupying a frequency band not broader than 10 % of its central frequency (justification of this threshold is provided below). For information, Annex A presents the operating system bands and channel bandwidths of several common wireless services. Wide-band communication systems, e.g., ultra-wideband (UWB) systems employing impulsive waveforms with fractional bandwidth well in excess of 10 %, are relatively new to the marketplace, have experienced limited deployment so far, and are not typically regarded as significant contributors to EM exposure levels due to low transmit power levels. NOTE Present exposure evaluation standards for fixed or mobile wireless communication devices, e.g., IEC 62209-1, are mostly tailored towards defining suitable techniques for narrowband waveforms. For instance, they recommend the use of scalar E-field or H-field sensors, e.g., miniature diode-detector probes, which typically provide accurate readings for narrowband waveforms, as defined herein. The paucity of UWB wireless communication systems, which have only very recently been introduced in the marketplace, as well as the low power levels associated with the corresponding signals to avoid interfering with coexisting electronic systems, has so far reduced the priority to standardize suitable evaluation techniques and to develop the relevant test instrumentation.