Speech and voice changes are a central feature of the symptom complex of people with Parkinson's disease (pwPD). Speaking is a social activity involving the pwPD, family, and the wider communicative context. Sensory-motor, cognitive-linguistic, and affective changes in Parkinson's disease (PD) combine to alter communication, impacting on psychosocial quality-of-life, leading to risks of social withdrawal and increased depression and anxiety. The underlying pathophysiology of speech, voice, and communication difficulties in pwPD is multi-factorial and complex. Sensory-motor changes in the respiratory, phonatory, and articulatory subsystems, underscaling of effort, and central processing problems are further affected by broader cognitive-linguistic difficulties, and non-speech motor deficits. Many studies show that, when pwPD are asked to rate their own voice and how it functions in everyday situations, they show increased voice-related disability and negative impact relative to healthy controls. Voice treatment is integral to improving communication in pwPD. Studies show positive benefits from the perspective of pwPD and carers. Treatment approaches vary from one-to-one to group interventions, a singular focus on increasing loudness to more general voice exercises, and choral singing. The nature and underlying pathophysiology of speech, voice, and communication changes in pwPD are reviewed before exploring the effects of voice treatment programs and pwPD and carer perceptions of their effect. Larger scale, better powered, controlled trials of intervention for voice and speech that measure clinically and socially relevant outcomes are finally underway. Future research should also focus on issues of treatment compliance, practicality (for service delivery and use), and long-term follow-up outcomes. The role of carers in longer-term maintenance represents a further important area of exploration.