This white paper provides a description of ultrasound imaging systems with focus on the signal processing strategies. The different system components are briefly discussed followed by a description of ultrasound related peculiarities that the system needs to handle. The system processing for B-mode imaging can be roughly divided into three components: the front end (that includes transmission, reception, and digitization of ultrasound signal), followed by beamforming (to focus on a particular scan line), the mid end (that performs demodulation, envelope detection, and compression), and finally, the back end (that performs various image enhancement and rendering functions). The processing required in Doppler mode is described and, finally, the processing and issues related to 3D/4D imaging using ultrasound systems are briefly discussed.