Single-molecule spectroscopy has profoundly transformed our understanding of chemical and biological systems, enabling us to visualize dynamic processes that are otherwise hidden in ensemble averages. Over the years, this approach has expanded from fundamental biophysics and catalysis to materials research, where nanoscale heterogeneity governs macroscopic function. In this lecture, I will illustrate how single-molecule and super-resolution microscopy, coupled to advanced spectroscopic and imaging modalities developed in our laboratory, are now used to unravel the photophysical complexity of metal halide perovskites. I will discuss how our recent work - ranging from blinking microscopy to strain-stabilized perovskite phases - has provided unprecedented insights into ion migration, lattice strain, and local phase instabilities. We demonstrate how correlative optical and structural imaging can reveal the interplay between local defects, composition, and emission properties, and how analysis of time-lapsed intensity mapping allows bridging the gap between molecular-scale fluctuations and device-scale performance. Finally, I will outline how these methodologies are driving the discovery of lead-free, broadband, and short-wave infrared (SWIR) emitters, opening pathways toward new optoelectronic and sensing applications. By connecting the precision of single-molecule spectroscopy with the complexity of functional materials, our work aims to show how “seeing the invisible” at the nanoscale can accelerate sustainable materials innovation.