This chapter provides propagation measurements to study the performance of indoor Wireless local area networks. Three different indoor environments were used in the propagation study; they will be referred to as Environments A, B, and C. Eight experiments that were conducted to study the impact on WLAN performance of radio propagation in Environment A. In Environment B, both ad hoc and infrastructure network scenarios were used to study the impact of the radio propagation environment on WLAN performance. The effect of line-of-sight (LOS) blockage by furniture and walls on transmission times as well as throughput of an 802.11b ad hoc WLAN is investigated in Environment C. The chapter discusses the effect of transmitter-receiver orientation on 802.11 link throughput. It explains the effect of office wall partitions on WLAN throughput. The chapter shows that the effect of LOS blockage on WLAN performance. It suggests that the effect of floors and single-wall separation on 802.11 link throughput and the effect of microwave oven interference on 802.11 networks.