This dissertation has impacted our understanding of the motor control strategies employed by infants with or at risk for CP during sitting development, and how these infants respond in their development of sitting postural control, in terms of coordination of the thorax and pelvis, if they receive a weekly home program versus a twice- weekly intervention from a physical therapist using a perceptual-motor intervention. Here we provide a quantitative description of the development of sitting posture in infants with or at risk for CP but also a valuable tool in assessing progress of infant sitting postural control in terms of segmental coordination in both typically developing infants and infants with or at risk for CP, which is sensitive enough to study the effect of therapeutic interventions directed at improving sitting postural control. This dissertation also evaluated the effect of the three major sensory systems (visual, somatosensory, vestibular) during sitting posture in typically developing infants. When somatosensory information is modified, greater complexity and more randomness is present in the COP time series, which allows for the discovery of successful strategies for maintaining sitting posture. Under dim light conditions typically developing infants present greater amount of variability along with more complexity and randomness present in the COP time series. This event demonstrates dissimilar plane (AP vs ML) control during infant sitting posture. COP nonlinear changes in both AP and ML direction were mostly induced due to the effect of the dim lighting on infant sitting posture, rather than the foam support surface. Combination of vestibular-ocular-reflex and posturography testing, such as the sitting paradigm presented here, could offer a complete description of vestibular function and an effective and quantitative way of studying therapeutic interventions directed at improving the postural control of infants with motor sensory disorders. We believe that through active exploration infants gain knowledge of how their actions produce changes to the incoming sensory information and vice versa, and create a sufficient internal model for the control of sitting posture as it has been shown previously with standing posture and walking.