The incidence of gastric cancer has been declining globally in the last decades. Despite the improvements in the diagnostic procedures, most cases are still detected at advanced stages due to lack of specific symptoms associated with early phases of tumour development. Consequently, gastric cancer poses a major health burden worldwide due to high mortality rates. Continuing advances in high-throughput technologies are revealing an intricate network of genetic and epigenetic changes associated with carcinogenesis. In addition, several risk factors, both environmental and genetic, have been recognized, which promote accumulation of diverse alterations affecting the expression of oncogenes, tumour suppressor genes, DNA repair genes, and other genes, implicated in normal gastric cell functions. A plethora of aberrant molecular events found in patients with this disease and intragenic heterogeneity of tumours from individuals are delaying the development of targeted biological therapies. Frequent occurrence of characteristic CpG island methylator phenotypes (CIMP phenotypes) in gastric cancers, particularly in association with Helicobacter pylori or EBV infection, could lead to introduction of epigenetic modulators into standard treatment regimens used against early and advanced forms of adenocarcinomas. This review highlights aberrant DNA methylation events in the development of gastric tumours and addresses the different aspects associated with the application of therapeutic epigenetic modulation in the management of the disease.