We present analytical, numerical and experimental studies of capillary ridges, that is, of long, narrow strips of liquid partially wetting a flat or curved substrate. Such thin film geometries possess both free boundaries and moving contact lines, and are known to display a large variety of instability phenomena. They provide an excellent example of the mechanism of dewetting due to capillary instability. Here, the possibility of dewetting and subsequent breaking of the continuous liquid strip into a sequence of droplets is essentially the result of flow induced by an excess of interfacial energies of the liquid/vapor, liquid/solid, and solid/vapor interfaces. We address two fundamental questions: (i) under what geometric and material conditions such solid/liquid configurations remain absolutely stable, and (ii) how the degree of contact line slip affects the liquid ridge morphological changes, dewetting growth rate, most unstable wavelength of instability, and long-term breakup times.