This dissertation investigates acoustic emission (AE) monitoring as a unified framework for characterizing failure processes across material systems and scales. Through controlled laboratory experiments of additive manufacturing and laboratory earthquake experiments, AE sensors are shown to distinguish between slow and rapid stress transfer processes, enabling signal identification, quantification, and localization.In additive manufacturing, AE monitoring differentiated tensile cracking from thermal expansion and powder effects, while porosity produced no detectable signals during laser spot welding. Using a calibration technique that uses a ball impact as a reference source, estimated crack sizes agreed with observations from scanning electron microscope images. Laboratory earthquake experiments investigated frictional heterogeneity using meter-scale Polymethyl methacrylate (PMMA) blocks in a biaxial testing machine. On frictionally heterogeneous faults, velocity-weakening (VW) regions with bare PMMA surfaces produced seismic slip, whereas velocity-strengthening (VS) regions coated with Teflon tape exhibited stable, aseismic slip. A single VW patch surrounded by VS regions exhibited systematic transitions: aseismic slip, periodic slip, and non-periodic slip, as identified through AE sensors. To create a more heterogeneous and realistic fault system, multiple VW patches separated by VS barriers were implemented. This fault configuration produced complex seismicity including foreshocks, mainshocks, and aftershocks. Varying the loading rate illuminated an inverse trend to fault healing (i.e., an increase in seismic magnitude over time) due to variations in VS barrier effectiveness with loading rate. Foreshock sequences, identified from the hypocenters determined by AE signals, and quasi-dynamic earthquake simulations both exhibited bidirectional migration with back-propagation velocities about ten times faster than the main propagation velocity, resembling Rapid Tremor Reversals in subduction zones. Fluid injection experiments using Teflon tape to confine flow revealed two migration mechanisms: pressure-diffusion-driven migration at slow injection rate or low-viscosity fluid, and volume-driven migration at fast injection rate or high-viscosity fluid. Poroelastic modeling reproduced experimental observations by coupling pressure-dependent permeability with fault opening. Together, these results demonstrate AE monitoring's capability to bridge material science and geophysics, providing insights into failure mechanisms from microstructural defects to earthquake dynamics across vastly different temporal and spatial scales.