BACKGROUND: Texting while walking (TeWW) has become common among people of all ages, and mobile phone use during gait is increasingly associated with pedestrian injury. Although dual-task walking performance is known to decline with age, data regarding the effect of age on dual-task performance in ecological settings are limited. OBJECTIVE: The objective of this study was to evaluate the effect of age, environment (indoors/outdoors), and mixed reality (merging of real and virtual environments) on TeWW performance. DESIGN: A cross-sectional design was used. METHODS: Young (n = 30; 27.8 ± 4.4 years) and older (n = 20; 68.9 ± 3.9 years) adults performed single- and dual-task texting and walking indoors and outdoors, with and without a mixed reality display. Participants also completed evaluations of visual scanning and cognitive flexibility (Trail Making Test) and functional mobility (Timed "Up & Go" Test). RESULTS: Indoors, similar interference to walking and texting occurred for both groups, but only older adults' gait variability increased under dual task conditions. Outdoors, TeWW was associated with larger age-related differences in gait variability, texting accuracy, and gait dual-task costs. Young adults with better visual scanning and cognitive flexibility performed TeWW with lower gait costs (r = 0.52-0.65). The mixed reality display was unhelpful and did not modify walking or texting. LIMITATIONS: Older adults tested in this study were relatively high functioning. Gaze of participants was not directly monitored. CONCLUSIONS: Although young and older adults possess the resources necessary for TeWW, older adults pay an additional "price" when dual-tasking, especially outdoors. TeWW may have potential as an ecologically valid assessment and/or an intervention paradigm for dual-task performance among older adults as well as for clinical populations.