The objectives and main aim of the work discussed in this chapter is to compare 2D with 3D surface roughness parameters measured on functional surfaces. The functional surfaces provided were automotive cylinder liners, steel sheet product and ball bearings. Tests designed to throw light on the dispersion and variability, when measuring and calculating 2D and 3D parameters, were also carried out. These results indicated the number of measurement needed for a surface to receive a stable mean value for the topography. Additionally, work is discussed which shows the functional relationship between traditional 2D surface parameters and a range of the newly developed 3D parameters. This study allowed a deeper understanding of the functionality of automotive cylinder bores, and empirical wear relationships are proposed. Finally, studies were carried out on sheet steel for the purpose of comparing optical and tactile measurement techniques