Interfaces play critical roles in governing chemical reactivity across many systems ranging from fuel cells to batteries to atmospheric aerosols, yet the molecular-level processes occurring at these boundaries remain poorly understood. This talk will highlight how spatially resolved techniques can provide detailed insights into two complex interfacial environments. In the first part of this talk, I will discuss how combining spatially resolved electrochemistry with complementary scanning probe methods reveals which sites in transition-metal dichalcogenides are electrocatalytically active and why. In the second part, I will show how confocal fluorescence microscopy can measure how molecules localize, orient, and react at gas–liquid interfaces, providing a molecular picture of interfacial reactivity.