Acoustic models of soft biological tissues are discussed. The methods to derive acoustic bulk parameters, i.e. attenuation coefficient and backscattering coefficient are outlined. When applying a specific backscattering model the effective dimension of the scattering sites within a tissue can be estimated. The texture of echographic images is defined in terms of speckle and it is discussed in which way the texture is influenced by the beam formation and the volume density of the scatterers. Structural characteristics of tissues are discussed and the method to estimate a structural dimension is indicated. Recent developments are parametric imaging and image processing.