This chapter examines the assessment and measurement of fatigue in Long COVID through both subjective and objective approaches. It analyzes various subjective fatigue scales, including the Fatigue Severity Scale (FSS), Fatigue Assessment Scale (FAS), Chalder Fatigue Scale (CFS), and Modified Fatigue Impact Scale (MFIS), while also exploring objective measures such as the Six-Minute Walk Test (6MWT), Cardiopulmonary Exercise Testing (CPET), Heart Rate Variability (HRV), and neuroimaging techniques. The text highlights emerging brain laboratory biomarkers in Long COVID, including tau, amyloid, light chains, lipids, proteins, and cytokines, and their role in understanding neurological and cognitive symptoms. Additionally, it discusses artificial intelligence applications in Long COVID diagnosis and assessment, particularly focusing on natural language processing and computer vision for medical imaging analysis. The chapter emphasizes the importance of integrating multiple assessment approaches, demonstrating how combining subjective scales with objective measures and AI-driven analysis provides a more comprehensive understanding of Long COVID fatigue. This multifaceted approach enables better diagnosis, monitoring, and treatment of fatigue symptoms, ultimately improving patient outcomes and quality of life.