Expandable stents are widely used in gastroenterology. The basic principle of all of these devices is that they can be constrained onto a delivery system of small diameter and then deployed in an area of stenosis without the risk of complications due to excessive dilation. Understanding tissue responses to stents is important both for the design of new stents and for clinicians to balance the benefits and risks of covered and uncovered stents. With biodegradable stents and removable stents, understanding tissue responses provides the basis for timing of removal and assessing treatment response.