From window materials to synthetic polymers, from fiber optics to proteins, glasses and their unique properties play a significant role in our daily lives. The molecular dynamics of proteins, glasses, and supercooled liquids are very different compared to smaller molecules or regular liquids. For example, molecular relaxation processes show a very strong (and unusual) non exponential response to perturbations. In the past few years the focus of research on these materials has gradually shifted from a macroscopic description of properties to their analysis on a molecular scale. One especially promising result explains their unusual properties as a consequence of a strong dependence of a molecule’s dynamics on the structure of its environment, a correlation often called “dynamic heterogeneity.” Our research pushes this molecular description of glass dynamics to its extreme: using single molecule spectroscopy to investigate glasses experimentally one molecule at a time along with molecular dynamics simulations on fast computers to study the theory of the glass transition at the same level of detail.