The thesis discusses the acquisition of three-dimensional information by means of the Intensity Ratio Depth Sensor. The Intensity Ratio Depth Sensor uses a structured-light triangulation approach for the measurement of depth from a camera unit to object surfaces in a scene. The device may be viewed as a modification of the plane-of-light scheme in which multiple illumination planes are encoded by intensity ratio values obtained from two or three intensity images. The modification avoids the need to scan the plane of light which, together with the small amount of processing required for the depth calculation, offers a distinct speed advantage over existing schemes. The system design and calibration issues, necessary in obtaining a working Intensity Ratio Depth Sensor, are analyzed. The depth equation (for the transformation of intensity ratio values into depth values) together with four experimental methods for its calculation are presented. The results of the four sensor implementations are given for test scenes. Potential scene dependent and scene independent error sources are discussed. In particular, mutual illumination (illumination resulting from reflections between surfaces elements) is an important scene dependent error source. An analysis of mutual illumination based on a radiative energy transfer formulation is presented. The result of the analysis is an iterative mutual illumination removal algorithm which is applied to test scenes. Two empirical methods for mutual illumination removal are also derived and demonstrated. Preliminary processing of the three-dimensional data produced by the sensor, exploiting constraints imposed by the device, is examined. The processing yields first and second derivative surface parameters for points in the scene.