K-Space is a frequency domain description of ultrasonic imaging systems and targets which can be used to gain insight into their interaction during image formation. Although originally proposed as a technique for the analysis of imaging problems involving anisotropic scattering, we have found it useful as a general analysis tool. We present analytical and conceptual techniques for estimating the k-space representation of imaging systems with arbitrary transmit and receive array geometries and apodizations. We describe simple graphical methods of estimating the first and second order characteristics of speckle formed using different imaging geometries. We also present examples utilizing k-space to gain intuition about the performance of spatial and frequency compounding and to describe the impact of several synthetic aperture geometries on beam forming and speckle statistics. We present the Van Cittert Zernike Theorem in k-space and discuss techniques which can be used to improve echo correlation.