Two hundreds years ago, Thomas Young understood how the solid/liquid contact is dictated by surface forces. Our plan is to discuss how the solid roughness modifies (quite dramatically) this law. Roughness can be either accidental, or set at a surface with micro-machined extures, which decides the resulting properties: super-hydrophilicity, water repellency, slip, anti-fogging properties, etc. We present recent developments in this lively field of surface science.