Electron tunneling is a powerful quantitative probe of the excitation spectrum of superconductors.  The scanning tunneling microscope (STM) is a convenient tool for measuring the tunneling spectrum at different spots on a superconducting sample, thus probing the spatial variations of the excitation spectrum. Such measurements have been used on the high-temperature superconducting cuprates, giving us an atomic scale view of the excitation spectrum. I will describe STM experiments performed as a function of temperature on samples of the cuprate Bi2Sr2CaCu2O8+x, with the aim of understanding how superconductivity develops in the material as it is cooled down from the “normal” state. By directly measuring the spectrum at different locations in space and at different temperatures, we come to the conclusion that superconductivity develops in a spatially inhomogeneous fashion in this compound. A detailed study of the shape of the spectrum as a function of doping and temperature gives us insight into the nature of the energy gap seen in the spectrum.