Body composition assessment is crucial in clinical nutrition practice for screening, diagnosis, treatment, and prognosis of patients. Bioelectrical impedance analysis (BIA) is widely used to assess body composition. Impedance devices measure the body's electrical response (resistance) when exposed to an electrical current, thereby indirectly estimating body composition by conducting a low electrical current into the body. However, multiple factors, including devices, equations, indices, and population references, affect the interpretation of BIA results. Bioelectrical impedance vector analysis (BIVA) has been developed as an alternative method for semi-quantitative assessment of hydration status, which overcomes some limitations of traditional BIA by analyzing vector distance patterns and their distribution on resistance and reactance (R-Xc). This review describes the BIA device classification, which is useful for determining when the BIVA approach is appropriate for body composition analysis. This narrative review outlines the requirements and medical and nutritional uses of bioelectrical impedance vector analysis in adult patients over the past decade. Several publications have reported the clinical applications of BIVA in adult patients, including the evaluation of fluid volume status, control of body fluids, and prediction of negative outcomes in patients undergoing renal replacement therapy or admitted to critical care units. It has also been used as an alternative diagnostic tool in adults with fluid abnormalities to detect sarcopenia, cachexia, or malnutrition, reflecting low body cell mass or a decrease in soft tissue. However, some implications must be considered to avoid affecting the interpretation of the results, including differences in devices, analysis methods, and specific population references. Thus, this review aims to describe the differences between the devices and analysis techniques used for BIVA, which will be discussed in this review.