There are various classifications of causes of intestinal obstruction. These are used for different reasons and there is marked overlap. The classification that is most helpful in describing the different causes is that based upon the location of the obstructing agent with reference to it being in the lumen of the bowel, in the wall of the bowel or on the outside. Classifications which are useful in clinical practice would include whether the obstruction is simple or complicated, whether there is a closed loop or not, whether it affects the small or large intestine. As usual it is also nice to know the common and rare varieties.