Science fiction promises that someday we will have machines that talk to us. With Siri on the iPhone and Watson beating human champions at Jeopardy, is that future finally here? Not yet because getting computers to truly understand language is hard, even though most 2-year-olds manage to do it as a matter of course. This lecture will introduce the science behind language technologies – including the central role of probability and statistics – and illustrate why understanding human language is still such a difficult problem.