The cold climate of the Arctic and sub-Arctic means that permafrost, permanently frozen ground, underlies large areas of the landscape. But as the climate warms, just how permanent is permafrost, and what happens when it begins to disappear? Permafrost temperatures continue to warm across the Arctic, and climate projections show that this trend will continue. Recent observations from the Geophysical Institute Permafrost Laboratory monitoring network in the Fairbanks area show that, in some areas, ground that used to freeze completely during the winter is now remaining thawed year-round. In this talk we will look at how permafrost temperatures have changed over recent decades in Interior Alaska and across the Arctic. We will take a journey underground and look at how permafrost can contain massive ice bodies that play an important role in how permafrost thaw impacts the landscape above. Lastly, we will consider what factors play the most influential roles in rate of permafrost thaw and what changes we can expect in coming decades.