An early and accurate diagnosis for Parkinson's disease (PD) is essential not only for improving prognostic outcomes but also for enabling timely therapeutic interventions. Nevertheless, achieving early diagnosis remains difficult because the characteristic symptoms of PD frequently overlap with those of other neurodegenerative disorders. In addition, current diagnostic approaches rely heavily on clinical evaluation, underscoring the need for more precise, objective methods. In this scenario, the discovery and validation of robust biomarkers have become increasingly important, as they can aid in differential diagnosis, track disease progression, and inform the development of personalized therapies-ultimately enhancing patient management and quality of life. This Reprint of the Special Issue of the International Journal of Molecular Sciences features four reviews and six original research articles that explore new challenges in understanding, diagnosing, and treating Parkinson's disease. The contributions in this issue cover a broad spectrum of topics, ranging from the identification of biochemical, genetic, and epigenetic biomarkers to the application of advanced approaches, including multi-omics integration, artificial intelligence, and functional imaging. Particular attention is also given to the innovative use of extracellular vesicles (EVs) and to emerging therapeutic strategies.