内科学是临床医学的一个专科，几乎是所有其他临床医学的基础，亦有医学之母之称。它的内容包含了对疾病的定义、病因学、致病机理、流行病学、自然史、症状、症候、实验诊断、影像检查、鉴别诊断、诊断、治疗和预后等。

内科学的方法是透过病史询问或面谈后，进行理学检查，根据病史与检查所见做实验诊断与影像检查，以期在众多鉴别诊断中排除可能性较低者，获得最有可能的诊断；获得诊断后，内科的治疗方法包含追踪观察、生活方式、药物、介入性治疗（如心导管、内视镜）等，根据病人的状况调整药物之使用，防止并处理副作用及并发症。

Internal medicine or general medicine (in Commonwealth nations) is the medical specialty dealing with the prevention, diagnosis, and treatment of adult diseases. Physicians specializing in internal medicine are called internists, or physicians (without a modifier) in Commonwealth nations. Internists are skilled in the management of patients who have undifferentiated or multi-system disease processes. Internists care for hospitalized and ambulatory patients and may play a major role in teaching and research.