Walking serves as an important source of information for the research of human movement and behavior. In fact, the observation of walking adaptation, in response to the surrounding environment, can reveal a great deal about our everyday activity, functioning and health. Although traditionally, the observation of walking – or gait - is primarily performed in a laboratory, the findings of Study Ⅰ highlighted the need for more ecologically valid protocols and analysis, not in gait laboratories. Therefore, this dissertation presents the measurement of gait in more ecologically valid settings using non-obstructive body-worn sensors, while incorporating three different constructs or paradigms. 1) Gait-quality - the measurement of how we walk. 2) Gait-quantity – the measurement of how much we walk. 3) The Dual Task paradigm – the measurement of cognitive and physical performance under conditions of multitasking, as compared to performance under single task conditions. Accordingly, the protocol for investigating the dual task effect on gait-quality was designed to reflect the everyday “dual task” setting (Study Ⅱ-Ⅲ). This was achieved by asking participants to walk over ground, as opposed to a treadmill, at a self-selected walking speed with minimal instruction regarding task completion (Study Ⅱ-Ⅲ), and further, through the selection of a secondary task that replicated an everyday dual task: mobile phone use while walking. Further consideration was given to ecological validity in the cross-sectional analysis of gait-quantity in the daily work setting of white- and blue-collar workers (Study Ⅳ). Gait-quantity, defined as the number of steps and the cadence at which the steps occurred, was divided according to work and leisure hours - hereafter referred to as work and leisure domains. This division more accurately reflected everyday behaviors. In addition, the domain of steps was suspected to have implications for the associations between walking and health. Gait-quality assessed using spatiotemporal stride parameters indicated significant changes in how young adults walked when using a mobile phone (Study Ⅱ). Walking speed, stride length and cadence all decreased while double support time increased. In addition, there was a clear increase in the relative variability of these parameters when using a mobile phone. Further assessment using the nonlinear analysis of trunk acceleration patterns, indicated that both walking speed instruction and the use of a mobile phone significantly affected walking (Study Ⅲ). The analysis of gait-quantity highlighted the importance of domain information on the quantity of walking in white- and blue-collar workers, and its associations with health (Study Ⅳ). When observed in more ecologically valid settings, the effect of mobile phone use on gait-quality appeared small, amongst young adults, while including domain information in the analysis of gait it was important for the quantity and association with health. In conclusion, future research should strongly consider the ecological validity when measuring these constructs and paradigms of human walking.