Monitoring walking can be used to assess disease progression. Monitoring walking can give an important indication of health status, disease progression and the effect of interventions on the wide range of conditions which have such a profound effect on people’s health and lead to considerable health expenditures. Designs can be either cross-sectional, in which different people at different stages of the disease are monitored at a similar time, or longitudinal, in which case the same people are monitored at different times. Gait analysis is based around the concept that walking is a cyclic activity and that measurements from a small number of cycles are representative of the gait pattern of an individual. Continuous monitoring is also useful to track the considerable variability that is inherent in functional walking. Sensor-based systems for monitoring walking offer potential for use in two areas of the health domain.