This review describes the most important macroscopic, histological, and molecular biological features of carcinomas of the esophagus, the gastroesophageal junction (GEJ), and the stomach. The three most frequent histological subtypes of upper GI tract carcinoma, ie, adenocarcinoma, squamous cell carcinoma, and small cell carcinoma, are considered. Important histological classifications of upper GI tract adenocarcinomas such as Lauren's classification and the World Health Organization (WHO) classification, as well as rare histological variants of esophageal and gastric cancer, are described. Routes of tumor spread and principles of tumor classification are outlined. Furthermore, descriptions of the immediate precursor lesions of upper GI tract carcinomas, ie, dysplasias, are included. Finally, somatic genetic and epigenetic changes, which are associated with tumor development in the upper GI tract, are discussed.