Let us start with a simple scenario: a man asks a woman "how high is Mount Everest?" The woman replies "29,029 feet." Nothing could be simpler. Now let us suppose that rather than standing in a room, or sitting on a bus, the man is at his desk and the woman is 300 miles away with the conversation taking place using e-mail. Still simple? Certainly--it happens every day. So why all the bother about digital (virtual, electronic, chat, etc.) reference? If the man is a pilot flying over Mount Everest, the answer matters. If you are a lawyer going to court, the identity of the woman is very important. Also, if you ever want to find the answer again, how that transaction took place matters a lot. Digital reference is a deceptively simple concept on its face: "the incorporation of human expertise into the information system." This lecture seeks to explore the question of how human expertise is incorporated into a variety of information systems, from libraries, to digital libraries, to...