In this chapter the authors develop the models of sea clutter that will provide a basis for our subsequent discussion and calculation of radar performance. As the authors saw in the previous chapter, a direct approach to the modelling of sea clutter provides many useful insights. Nonetheless the interactions between the ocean, atmosphere and microwave radiation are far too complicated to be described usefully in strictly deterministic terms. Consequently the models we develop in this chapter are unashamedly statistical in character. The development of these statistical models is driven by the observations of real sea clutter described in Chapter 2, where it was noted that low-resolution, spatially uniform, clutter has Gaussian amplitude statistics. By introducing a simple random walk model for the clutter process we can construct this familiar Gaussian (Rayleigh) model for low-resolution sea clutter from first principles and characterise its interaction with target returns. This analysis, in turn, can be modified to take account of the effects of increased radar resolution; in this way we are led to the K distribution and related models. An advantage of this approach is that it demonstrates clearly how performance analysis germane to low resolution Rayleigh clutter can be extended quite straightforwardly to the K-distributed case. These few simple principles under pin much of the radar performance analysis presented in the rest of this book.