Walking requires two capabilities: maintenance of balance (protection of upright stance via anticipatory and reactive postural mechanisms) and movement through the environment via locomotion. Postural responses and locomotion are dependent upon all levels of the nervous and musculoskeletal systems. Consequently, gait and balance disorders are common manifestations of many diseases.

The clinician commonly thinks of gait disorders in terms of walking pattern, emphasizing the movements of the legs. And literally this is correct; ‘gait’ is defined by Webster's Third International Dictionary as the ‘manner of walking’ or ‘sequence of foot movements.’ Accordingly, the neurological exam emphasizes evaluation of strength, tone, coordination, sensation and reflexes of the limbs. The result is that clinical neurology focuses on locomotion.

The importance of balance or equilibrium to walking is not recognized or explicitly acknowledged. Yet balance is the key and critical element in safe ambulation. Many socalled gait disorders are in reality balance disorders, not disorders in the sequence of foot movements. For example, Bruns’ ‘frontal ataxia’ (Bruns, 1892) and van Bogart and Martins’ ‘apraxia of gait’ (1929) are descriptions of patients who could not even stand independently. Although impairments of gait or locomotion can sometimes be separated from impairments of balance or postural equilibrium, locomotion and balance are more often inextricably intertwined (Mori, 1987). Thus, classifications need to consider disorders of both gait and balance.

The aim of this chapter is to present a classification scheme for gait and balance disorders. We first consider a classification based on neurological functions required for purposeful ambulation using Hughlings Jackson's hierarchical scheme of lower, middle and higher functions. This classification suggests the range of neurological impairments that can disrupt ambulation and the relationships among various gait and balance disorders.

Patients’ walking and balance patterns do not necessarily reflect impairments in neural functioning but rather the patient's compensatory strategies for coping with the impairments. Different impairments may elicit common compensatory strategies. For this reason, classification by impairments is inadequate for clinical diagnosis. The second portion of our classification scheme considers the common compensatory strategies as clinical patterns or syndromes for which there are differential diagnoses. Problems with ambulation are separated into clinical patterns or syndromes that are predominantly disorders of balance and those that are predominantly disorders of locomotion, recognizing that in most diseases, both postural control and locomotion are affected to some extent.