Gastric cancer afflicts 27,000 Americans annually and carries a dismal prognosis. One reason for poor outcomes is late diagnosis, as the majority of gastric cancers in the United States are diagnosed at a relatively advanced stage where curative resection is unlikely. Gastric precursors (such as atrophic gastritis and intestinal metaplasia) are precancerous changes to the stomach mucosa which increases risk for subsequent gastric cancer. The Gastric Precancerous Conditions Study (GAPS) is an observational study of patients at elevated risk for gastric cancer. Investigators seek to recruit patients from endoscopy unit of Stanford Health Care, a large academic network of hospitals and clinics serving Northern California. Investigators will recruit patients who are both symptomatic (e.g. dyspepsia) and asymptomatic (e.g. referred for screening), and individuals both with known precursor lesions (such as intestinal metaplasia) or at high risk for carrying precursor lesions. A component of the study is long-term follow-up of individuals with gastric precursors. This is to understand their risk factors for histologic progression and regression. During both index and subsequent endoscopies, the study team will collect biospecimens (e.g. blood, saliva, gastric tissue).