Frictional slip between bodies having different elastic or geometrical properties (bimaterial interfaces) creates a unique type of rupture, bimaterial “slip pulses.” These slip pulses propagate along the interfaces separating elastically different contacting bodies. They exhibit highly localized slip with accompanying local normal stress reduction. These pulses do not result from properties of “friction laws” but, instead, are formed via the elastic mismatch of the contacting bodies. Here, we experimentally study slip pulse dynamics, evolution, and structure in seven different bimaterial interfaces. We find that slip pulses are a major vehicle for frictional motion in bimaterial interfaces, they exist in well-defined velocity windows and undergo unstable growth consistent with theoretical predictions coined the “Adams instability.” When scaled properly, slip pulses exhibit both universal spatial structure and growth dynamics. While slip pulse amplitudes vary considerably within different interfaces, this variation is, surprisingly, not highly dependent on the contrast of the elastic properties of the contacting materials. Instead, slip pulse amplitudes are closely related to the interfaces’ aging properties and, hence, to material plasticity at the interface. As bimaterial interfaces are generic, these results are fundamentally important to both frictional dynamics and the dynamics of earthquakes within a wide class of natural faults. Frictional slip is mediated by rapid rupture modes that enable motion (slip) along the interface that separates contacting elastic bodies. One often-studied situation is when the contacting bodies are composed of the same elastic material, a “homogeneous” interface. Recent experimental studies ( 1– 4) have shown that homogeneous interfaces separate by means of rupture modes, analogous to shear cracks, that detach the contacting surfaces to enable slip. These rupture (or “crack”) velocities are either bounded by the material’s Rayleigh wave speed or become supershear, propagating beyond the material’s shear wave speed ( 5– 7). Sub-Rayleigh cracks are characterized ( 8) by putatively singular stresses that are regularized at their tip in a small dissipative region, called the “cohesive zone.” Behind a crack’s cohesive zone, slip extends over large distances, with slip velocities decaying as 1 r with the distance, r , from the tip.