Freezing and festination during gait are common yet poorly understood motor control deficits in people with Parkinson's disease (PD). As a basis for evidence based clinical decision making during rehabilitation, we explore the underlying factors associated with freezing of gait in PD. It is argued that disorders of motor set and the sequence effect (festination) are associated with freezing, either in isolation or in combination. The contribution of environmental constraints, task related factors, attention, mental status, and prolonged use of PD medications are also investigated. On the basis of these findings, we propose strategies to reduce the frequency and severity of freezing episodes for a range of locomotion tasks.