Body composition assessment is essential in both clinical and field settings to accurately describe and monitor nutritional status for a variety of medical conditions and physiological processes. Patients with cancer, osteoporosis, cardiovascular disease, diabetes, as well as sick and malnourished patients, pregnant women, nursing mothers, and the elderly, are a few examples among several other diseases that can be assessed by body composition. Body composition outcomes help evaluate the effectiveness of nutritional interventions, the alterations associated with growth and disease conditions, and it contributes to the development of personalized physical training programs (1–3). There are several techniques for assessing body composition, from simple body indices based on anthropometric measurements to sophisticated laboratory methods such as magnetic resonance imaging (4), with the ability to assess different body compartments at different levels (5, 6). Thus, many studies have been conducted in order to develop and validate techniques, which can be extremely useful for health professionals to estimate body composition components such as fat mass, muscle mass, bone mass, and residual mass, or simply fat mass and fat-free mass (7–10). The aim of this Research Topic is to address the most recent innovations in body composition assessment for its application in epidemiological studies, as well as in clinical practice, providing health professionals with concepts and evidence of its usefulness, while assisting them with the most appropriate selection of techniques according to the characteristics of the individuals or groups evaluated.