A nurse on an acute care hospital ﬂoor wheels her medication cart into a patient’s room, careful not to jostle the laptop and radio frequency scanner that sit on top of the cart. She parks her cart, taps the icon on the touch screen of the computer that opens the bar code medication program, and logs into the program. She then scans the patient’s identiﬁcation number and, in response, the bar code medication program displays the patient’s record-a list of his prescribed drugs for this scheduled medication pass. One by one, the nurse takes the patient’s drugs from a cart drawer and scans the bar code of each. As soon as a bar code matches a prescription for this patient ID, the system “bings,” marks the drug approved on the screen, and documents the match, presuming it to be an accurate and successful drug administration. All eight medications for this patient “bing” positively. The nurse ﬁlls a cup with water, gives it to the patient along with his pills, and closes his record. The process took moments; the right patient got the right drugs at the right time and place; and the nurse moves on.