The genomic DNA in our cells, approximately 2 meters long, is packaged into a tiny nucleus of 5-10 micrometers in diameter, through DNA-protein complex known as chromatin. Chromatin organization plays an important role in regulating gene expression and is often disrupted in cancer cells. Abnormal chromatin structure has long been used to diagnose cancer. But due to the diffraction-limited resolution of conventional light microscopy, the detectable abnormal structures are limited to micro-scale features, thus hampering our ability to detect early-stage carcinogenesis or distinguish aggressive from indolent pre-cancerous lesions. Recent advances in super-resolution microscopy have significantly advanced our ability to interrogate the spatial organization of molecular structure down to ~20-30 nm. I will present our recent progress in developing super-resolution imaging techniques to visualize higher-order chromatin organization in cells and tissue, and its application to understand how nanoscale chromatin organization is altered in cancer development.