The Wireless Local Area Networks (WLANs) are often used as a wireless extension to the typical office network infrastructure providing mobility to the users. In addition Wireless Personal Area Networks (WPANs) serve interconnection to computer and mobile phone peripherals as headsets, input devices, printers etc. Thus it is common that WLANs and WPANs have to operate in the same area. IEEE 802.11b/g is the most popular WLAN technology operating in the 2.4GHz Industrial Medical and Scientific (ISM) band. On the other hand Bluetooth (BT) is the technology often used to support WPANs. As BT also uses the 2.4GHz ISM band, there an issue of interference between WLANs and PANs. In this work the performance degradation in Wireless Local Area Networks and Wireless Local Area Networks due to coexistence is examined by real measurements. Both 802.11 to 802.11 and 802.11 to Bluetooth coexistence is addressed.