Declarative UI is a way of making fluid user interfaces by describing them in terms of simple elements (Text, Image, Rect,and other QObjects) that are built up into components. The reason it is "declarative" is that rather than the changes in the UI being expressed as imperative code, they are instead expressed as sets of QObject property expressions, grouped into states. The fluid part comes from animated transitions between the sets of properties. Combined with Qt's signals and slots, a little bit of script for the tricky parts, and a rich collection of fluid UI elements, the result is a very powerful technology for making very cool looking UIs that are enjoyable to use.