Presents three essays about the area of mixed-initiative interaction. The first essay introduces the area and creates a useful taxonomy of mixed-initiative dialog issues. The author summarises several years' worth of research on mixed-initiative planning systems. The second essay describes the role of uncertainty in mixed-initiative interaction and describes two innovative systems for semi-automated assistance that make use of Bayesian reasoning. The final essay confronts the difficult task off evaluating such systems, including the creation of test sets and metrics for evaluating descriptive versus prescriptive dialogue models.