Abstract: Traditional text input modalities, namely keyboards, are often not appropriate for use when standing in front of very large wall displays. Direct interaction techniques, such as handwriting, are better, but are not well suited to situations where users are not in close physical proximity to the display. We discuss the potential of mid-air interaction techniques for text input on very large wall displays, and introduce two factors, distance-dependence and visibility-dependence, which are useful for segmenting the design space of mid-air techniques. We then describe three techniques that were designed with the goal of exploring the design space, and present a comparative evaluation of those techniques. Questions raised by the evaluation were investigated further in a second evaluation focusing on distance-dependence. The two factors of distance- and visibility-dependence can guide the design of future text input techniques, and our results suggest that distance-independent techniques may be best for use with very large wall displays.