A large part of patients admitted to hospital are undernourished and managed without nutritional support because of physician's failure to assess the nutritional state of patients. Therefore, nutritional screening and assessment of patients for malnutrition could be key to improving the treatment outcomes. It is the aim of this paper to inform the concept of nutritional screening and assessment, and introduce tools for general use. Several tools such as nutritional risk screening 2002, nutritional risk classification and others are available for nutritional screening. A recent change of weight, diet history, and the level of serum albumin are mainly included in these assessment tools. After an evaluation using screening tools, physicians can decide whether to start nutritional support or perform nutritional assessment in addition. Subjective global assessment (SGA), developed in 1987, has been mainly used for nutritional assessment. This tool takes into account the past history about the diet, weight variation, the degree of individual activity and fever. Several clinical studies have supported the efficacy of SGA to predict nutritional outcomes. Physicians should devise a plan for nutritional support based on the results of nutritional assessment. In conclusion, nutritional screening and assessment is essential for the evaluation of the patients who require medical or surgical intervention, because the patient's nutritional state can affect treatment outcomes. Therefore, physicians must take care to assess the nutritional state of patients before treatment using appropriate tools. Moreover, the most appropriate tool for nutritional assessment of Korean patients should be suggested through clinical studies. (JKSPEN 2013;5(1):2-9)