This paper investigates the impact of radio interference on the performance of an IEEE 802.15.4/ ZigBee communication link in an office environment. S-parameter measurements at frequencies around 2.405 GHz and with 3 MHz bandwidth, indicate level fluctuations of approximately 30 dB, caused by the propagation characteristics and multi-path fading within the room. Comparison between the fading characteristics of the room and the ZigBee packet error rate in the absence of interference indicates that errors occur when the path loss exceeds 55 dB, a level observed in less than 1% of scanned locations. Three types of interfering signals were generated within the room: band-limited additive white Gaussian noise (AWGN) centred at 2.405 GHz, a Bluetooth standard compliant signal and a WLAN (802.11.g) link. AWGN interference exceeding 15 dBm (total radiated power from the source causes the 802.15.4 link to suffer significant packet errors. The 802.15.4 link shows minimal observable packet loss in the presence of bursty Bluetooth. A study on coexistence between ZigBee and an actual IEEE 802.11g WLAN deployment shows that the degradation of the ZigBee link is approximately 50% and the net throughput of the WLAN link reduces by approximately 90%.