Susceptibility-Weighted Imaging (SWI) is a new neuroimaging technique that uses differences in magnetic susceptibility between tissues to generate unique contrast, different from spin density, T1, T2, and T2* weighting. This review discusses the technical background and clinical applications of SWI. SWI is based on gradient-echo imaging, which allows for the measurement of local susceptibility changes. The technique involves transforming magnitude and phase images into SWI data, with the filtered phase image used to visualize and quantify iron in the brain. Proper interpretation of SWI data is essential, and recommended sequence parameters are provided for different field strengths. SWI enhances contrast by detecting susceptibility differences, such as those from deoxygenated blood, hemosiderin, and ferritin. It is particularly useful for detecting iron in the brain, which is relevant for conditions like multiple sclerosis, stroke, and tumors. SWI has been developed over the past two decades, with significant technical advancements leading to its adoption in clinical settings. The technique involves using high-resolution gradient-echo sequences and post-processing methods like high-pass filtering to enhance susceptibility contrast. SWI combines magnitude and phase images to create a new susceptibility-weighted magnitude image. This image provides detailed information about tissue susceptibility, including iron content. The phase image is sensitive to local susceptibility changes and can be used to detect small vessels and microbleeds. SWI is particularly useful for visualizing vascular structures and has applications in stroke assessment, brain tumors, and other neurological conditions. The technique involves using a high-pass filter to remove background field effects and enhance susceptibility contrast. The phase mask is used to suppress unwanted phase information and enhance the contrast between tissues. SWI has been shown to be effective in detecting small vessels and microbleeds, and its use is expanding to other areas such as spine imaging and atherosclerosis. The technique is also being explored for quantifying oxygen saturation in major veins and monitoring changes in iron deposition over time. SWI is a valuable tool in neuroimaging, providing detailed information about tissue susceptibility and vascular structures. It is particularly useful for detecting iron in the brain and has applications in various neurological conditions. The technique is being further developed and optimized for use in clinical settings, with ongoing research into its potential for future applications.Susceptibility-Weighted Imaging (SWI) is a new neuroimaging technique that uses differences in magnetic susceptibility between tissues to generate unique contrast, different from spin density, T1, T2, and T2* weighting. This review discusses the technical background and clinical applications of SWI. SWI is based on gradient-echo imaging, which allows for the measurement of local susceptibility changes. The technique involves transforming magnitude and phase images into SWI data, with the filtered phase image used to visualize and quantify iron in the brain. Proper interpretation of SWI data is essential, and recommended sequence parameters are provided for different field strengths. SWI enhances contrast by detecting susceptibility differences, such as those from deoxygenated blood, hemosiderin, and ferritin. It is particularly useful for detecting iron in the brain, which is relevant for conditions like multiple sclerosis, stroke, and tumors. SWI has been developed over the past two decades, with significant technical advancements leading to its adoption in clinical settings. The technique involves using high-resolution gradient-echo sequences and post-processing methods like high-pass filtering to enhance susceptibility contrast. SWI combines magnitude and phase images to create a new susceptibility-weighted magnitude image. This image provides detailed information about tissue susceptibility, including iron content. The phase image is sensitive to local susceptibility changes and can be used to detect small vessels and microbleeds. SWI is particularly useful for visualizing vascular structures and has applications in stroke assessment, brain tumors, and other neurological conditions. The technique involves using a high-pass filter to remove background field effects and enhance susceptibility contrast. The phase mask is used to suppress unwanted phase information and enhance the contrast between tissues. SWI has been shown to be effective in detecting small vessels and microbleeds, and its use is expanding to other areas such as spine imaging and atherosclerosis. The technique is also being explored for quantifying oxygen saturation in major veins and monitoring changes in iron deposition over time. SWI is a valuable tool in neuroimaging, providing detailed information about tissue susceptibility and vascular structures. It is particularly useful for detecting iron in the brain and has applications in various neurological conditions. The technique is being further developed and optimized for use in clinical settings, with ongoing research into its potential for future applications.