Our surveys for extra-solar planets have revealed thousands of worlds that are strange to us dwellers of the Solar System. They include hot Jupiters and planets with sizes between that of the Earth and Neptune whose nature is still a mystery to us. But all of these worlds share something in common: they experience atmospheric loss at some point in their evolution. In this talk, I will show how we can use observations of mass loss in these exotic worlds to interpret the demographics of exoplanets. I will also discuss strategies to leverage the wealth of information contained in archival observations to understand how exoplanet atmospheres evolve. Ultimately, the physics involved in the interpretation of these observations will help us find out if planets orbiting stars cooler than the Sun are potentially habitable.