Frictional interfaces are abundant in engineering systems and consequently play a central role in determining their structural integrity. Recent experimental discoveries have revealed rich spatio-temporal dynamics that precede the onset of sliding motion. In this talk we will highlight novel features of frictional constitutive laws – most notably a transition from velocity-weakening friction at small slip velocities to velocity-strengthening friction at higher velocities – and theoretically explore their implications on the stability and failure of frictional interfaces. We demonstrate the existence of new steadily propagating rupture modes and quantitatively study their spontaneous emergence via frictional instabilities. Finally, we discuss the appearance of high frequency instabilities in the velocity strengthening regime.