[en] There is a need to be able to quantify how sound is reflected from a surface, in terms of how it is spatially dispersed. In recent years, diffusion and scattering coefficients have been developed to enable room acoustic prediction models to be more accurate, and designers to evaluate the worth of diffusing surfaces. Two coefficients have been, or are about to be, enshrined in standards. With two coefficients being standardised, there is great potential for confusion. This paper is intended to bring together authors from different areas to explain where the coefficients should and should not be applied. In addition, this tutorial paper will revisit the rationale behind the coefficients and contrast the coefficient definitions and performance.