Work on Expert Systems has received extensive attention recently, prompting growing interest in a range of environments. Much has been made of the basic concept and the rule-based system approach typically used to construct the programs. Perhaps this is a good time then to review what we know, assess the current prospects, and suggest directions appropriate for the next steps of basic research. I'd like to do that today and propose to do it by taking you on a journey of sorts, a metaphorical trip through the State of the Art of Expert Systems. We'll wander about the landscape, ranging from the familiar territory of the Land of Accepted Wisdom, to the vast unknowns at the Frontiers of Knowledge. I guarantee we'll all return safely, so come along...