Imagine if, before you ever took a drug, doctors could predict which drug would work best for you, because they already had information on how organs in your body were likely to respond. Organs-on-a-chip research is bringing that day closer. This emerging technology allows scientists to watch the cascade of events that takes place in organs in response to drugs or during disease. Organs-on-chips are 3-D biochips, no bigger than a computer memory stick, that contain living human cells from an organ or tissue. Engineered in layers and channels, substances such as air or blood can be delivered continuously, and the cells can interface with other living tissues as they do in the body.