The report aims at giving an overview of current system development concerning wall-penetrating radar. The information has been gleaned from various journals, proceedings and Internet searches. More recent references have been given priority over older ones. The report is primarily directed towards system development but considers some interesting experimental results obtained with test equipments. A few works concerning simulation/modeling are commented. A summary account is given of publications containing experimental determination of the transmission properties of various types of wall material. The report also describes the activity concerning wall-penetrating radar at the Sensor Technology Division of FOI at Linköping. Finally, conclusions are drawn about the analysis of the activities in the outside world. Considering the pressing international need for systems for the detection of humans through walls it is noteworthy that up to now only one operative system has been developed: RadarVision/SoldierVision. An important observation is that the system work and experimental results of FOI Sensor Technology concerning wall penetrating radar hold their own also in international comparison.