Over the recent years, intestinal absorption has been recognized as a critical factor affecting the bioavailability of oral drugs. Intestinal absorption is affected by many factors including the physicochemical property of the drug, the absorption mechanisms, and the need for absorption enhancers. Ex vivo and in situ methods have been used extensively to evaluate the intestinal absorption of new drugs. Biological performance can be obtained rapidly and reliably using these techniques. However, these approaches have many inadequacies which need to be recognized so that appropriate adjustments can be made to the methodology. These shortcomings also need to be accounted for during the interpretation and application of the results in vivo situations. This review describes ex vivo and in situ models of drug absorption, and compares their relative advantages and drawbacks to assist researchers in selecting appropriate models for different drug and therapeutic situations.