There is increasing demand for three-dimensional (3D) medical ultrasound imaging; compared to conventional two-dimensional (2D) ultrasound imaging, 3D ultrasound imaging simplifies examinations and provides better quantitative data. High-quality 3D ultrasound imaging depends on large 2D arrays of ultrasound transducers. Compactly connecting to a 2D transducer array and achieving good receive sensitivity requires a close connection between the transducer array and electronics. This thesis examines the design of integrated circuits (ICs) for 3D ultrasound imaging and their integration with 2D capacitive micromachined ultrasonic transducers (CMUTs). The successful flip-chip bonding of a 16×16-element CMUT array to a singlechannel custom-designed IC demonstrates an integrated 3D ultrasound imaging system. The IC provides each element of the array with a 25-V unipolar pulser and a transimpedance amplifier. Characterization of flip-chip bonded devices shows 100% yield, 125% fractional bandwidth, 339 kPa transmit pressure, and 1.2 mPa/√Hz input-referred noise. Three-dimensional images reconstructed using classic synthetic aperture imaging demonstrate the imaging capability of the device. Additionally, acquired photoacoustics images demonstrate the device’s utility for the emerging field of photoacoustics imaging. Compared to a single-channel system, using multiple elements in parallel for both transmit and receive improves image contrast and signal-to-noise ratio (SNR). Simulated point spread functions (PSFs) for a 16×16-element array show that using the 32 elements along the array diagonals for receive and the remaining elements for transmit (FT-XR-NC) results in a PSF comparable to the one obtained when using the full array for both transmit and receive. An IC with programmable delays and 16 parallel receive channels implements the FT-XR-NC array design. Measurements of pulser output voltages and the sound pressure level at the focal point show that the pulser delays have about 5 ns accuracy and that the IC can generate arbitrarily focused ultrasound beams. Images acquired of a latex heart phantom demonstrate the IC’s imaging capability. The work presented in this thesis shows a reliable method for connecting an integrated circuit to a 2D CMUT array for 3D ultrasound imaging. Characterization of CMUT arrays flip-chip bonded to custom-designed integrated circuits demonstrate 3D imaging capability, high yield, good receive sensitivity, and the wide bandwidth of micromachined ultrasonic transducers.