Recently, a survey was conducted for the Joint Project Steering Group (JPSG) of the National Institute of Justice (NIJ) and Defense Advanced Project Research Agency (DARPA)to determine the state-of-the-art at the present time in through-the-wall surveillance (TWS) technology and the expected advances within the next 10 years. The applicable technologies for TWS include: impulse radar, UHF/microwave radar, millimeter wave radiometry, x-ray transmission and reflectance, and acoustics. Proposed sensors include: monostatic radar, bistatic (or multistatic) radar, radiometers, fixed antenna systems, scanning systems, and focal plane array systems. The ability to penetrate walls leads to a natural conflict between the desire to successfully penetrate walls, which implies lower frequencies and the desire to obtain maximum resolution, which implies higher frequencies. Another conflict involves sophistication of the sensor versus unit cost. These issues and the approaches taken by various developers to find workable solutions are discussed.