Lewy body dementias encompass Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB), both characterized by the presence of Lewy bodies and Lewy neurites resulting from α-synuclein aggregation. Clinical variations in these diseases stem from differing pathological locations and severity, along with the co-occurrence of Alzheimer’s disease pathology. Consequently, there is a pressing need for biomarkers capable of early detection, distinguishing individuals with Lewy body dementias from other neurodegenerative disorders, and capturing co-existing pathologies. The chapter begins by exploring clinical diagnostic categories within the Lewy body disease spectrum and evaluating existing biomarkers integrated into diagnostic criteria. The discussion then delves into ongoing research on these biomarkers and emerging alternatives. Future directions include identifying early disease markers and predicting progression in line with recent prodromal PD and DLB research criteria. Furthermore, research suggests that factors such as inflammation, gut-brain-axis dysfunction, and cerebrovascular issues play a role in Lewy body diseases, and quantifying these markers may be an important future direction.