This chapter provides an overview of multiple sclerosis (MS), a common inflammatory, demyelinating, and neurodegenerative disorder of the central nervous system (CNS). MS affects approximately 2.5 million individuals worldwide, with women being twice as likely to be affected as men. The clinical manifestations of MS are highly variable, often starting with vision loss due to optic neuritis. Physical and cognitive disabilities are common, and the severity of these symptoms can be assessed using scales such as the Kurtzke Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Functional Composite (MSFC). The clinical course of MS can be categorized into relapse-remitting (RR), secondary-progressive (SP), primary-progressive (PP), and progressive-relapsing (PR) subtypes. MRI has played a crucial role in diagnosing and understanding MS, particularly in visualizing white matter (WM) and gray matter (GM) lesions. The detection of WM lesions has been straightforward, but GM lesions, especially those in the cortex, were initially challenging to visualize due to their low myelin content and small size. Advanced MRI techniques, such as fluid-attenuated inversion recovery (FLAIR) and double inversion recovery (DIR), have improved the detection of cortical lesions. Higher magnetic field strengths (e.g., 3T and 7T) have further enhanced lesion detection and characterization, allowing for better differentiation between different types of lesions. The underlying mechanisms of MS involve genetic and environmental factors, with the HLA-DRB1*1501 gene being a significant susceptibility factor. Pathologically, MS is characterized by demyelination, axonal loss, and gliotic scar formation. Quantitative MRI techniques, such as magnetization transfer ratio (MTR) and quantitative R2*, have shown promise in detecting small changes in tissue properties that correlate with clinical outcomes. The thesis aims to improve the visualization and characterization of GM and WM tissue abnormalities in MS using advanced MRI techniques, explore genetic and clinical correlates of these changes, and investigate the potential of MRI for early pathology detection and phenotyping. The chapters cover the visualization and characterization of lesions at standard and ultra-high field strengths, the role of quantitative MRI, and the relationship between MRI measures and clinical outcomes.This chapter provides an overview of multiple sclerosis (MS), a common inflammatory, demyelinating, and neurodegenerative disorder of the central nervous system (CNS). MS affects approximately 2.5 million individuals worldwide, with women being twice as likely to be affected as men. The clinical manifestations of MS are highly variable, often starting with vision loss due to optic neuritis. Physical and cognitive disabilities are common, and the severity of these symptoms can be assessed using scales such as the Kurtzke Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Functional Composite (MSFC). The clinical course of MS can be categorized into relapse-remitting (RR), secondary-progressive (SP), primary-progressive (PP), and progressive-relapsing (PR) subtypes. MRI has played a crucial role in diagnosing and understanding MS, particularly in visualizing white matter (WM) and gray matter (GM) lesions. The detection of WM lesions has been straightforward, but GM lesions, especially those in the cortex, were initially challenging to visualize due to their low myelin content and small size. Advanced MRI techniques, such as fluid-attenuated inversion recovery (FLAIR) and double inversion recovery (DIR), have improved the detection of cortical lesions. Higher magnetic field strengths (e.g., 3T and 7T) have further enhanced lesion detection and characterization, allowing for better differentiation between different types of lesions. The underlying mechanisms of MS involve genetic and environmental factors, with the HLA-DRB1*1501 gene being a significant susceptibility factor. Pathologically, MS is characterized by demyelination, axonal loss, and gliotic scar formation. Quantitative MRI techniques, such as magnetization transfer ratio (MTR) and quantitative R2*, have shown promise in detecting small changes in tissue properties that correlate with clinical outcomes. The thesis aims to improve the visualization and characterization of GM and WM tissue abnormalities in MS using advanced MRI techniques, explore genetic and clinical correlates of these changes, and investigate the potential of MRI for early pathology detection and phenotyping. The chapters cover the visualization and characterization of lesions at standard and ultra-high field strengths, the role of quantitative MRI, and the relationship between MRI measures and clinical outcomes.