Speckle appearing in synthetic aperture radar (SAR) images is due to the coherent interference of waves reflected from many elementary scatterers [1]. This effect causes a pixel-to-pixel variation in intensities, and the variation manifests itself as a granular noise pattern in SAR images. Speckle in SAR images complicates the image interpretation and image analyses, and reduces the effectiveness of image segmentation and feature classification. Understanding SAR speckle statistics is essential for better information extraction by designing intelligent algorithms for speckle filtering, geophysical parameter estimation, and land-use, ground cover classification, etc. In this chapter, speckle statistics of a single polarization SAR will be discussed first for both single- or multilook averaged data. The statistics of polarimetric and interferometric SAR data will be followed, emphasizing the complex Wishart distribution for the polarimetric covariance or coherency matrices. The phase difference, amplitude product, and amplitude ratio between two polarizations are important discriminators for terrain classification and geophysical parameter estimation. Their distributions are derived from the complex Wishart distribution, and they will be discussed in detail. For verification of these probability density functions (PDFs), polarimetric SAR data from NASA/JPL AIRSAR will be used. For heterogeneous media, SAR speckle statistics are better modeled by K-distributions. They will be discussed for both single polarization and polarimetric SAR data.