Permafrost underlies about 1/8 of the global exposed land surface and nearly half of the Canadian exposed land surface. To the casual observer, it is usually invisible. Driven by anthropogenic climate change, permafrost thaw will result in pervasive and persistent changes that will shape polar and high-elevation areas for decades and centuries to come. This presentation introduces permafrost as a research topic and highlights research avenues for measuring its thaw, i.e. the progressive melt of ice in the ground.