Oesophagogastroduodenoscopy (OGD) is invasive, may be poorly tolerated and is not without risk. Meanwhile, capsule endoscopy is well tolerated and adaptable to upper gastrointestinal (GI) territory. The null hypothesis of my thesis is that there is no role for capsule endoscopy in the investigation of the upper GI tract. The aim was to reject the null hypothesis using five studies. Chapter 3: A retrospective cohort study of 500 patients undergoing OGD for dyspepsia. Diagnoses made endoscopically or histologically that would not have been adequately managed by Helicobacter pylori testing (and treating if positive) and trial of a proton pump inhibitor were only seen in 16.2%. Chapter 4: A prospective cohort study of 156 patients assessing the tolerance and acceptability of OGD. More than 59% were worried about and 36% experienced significant gagging, choking and discomfort related to endoscopic intubation of the oropharynx. Despite this most patients regarded OGD as acceptable. Chapter 5: A prospective cohort study of 49 patients with recurrent or refractory iron deficiency anaemia. Magnetically assisted capsule endoscopy (MACE) by manipulating a capsule inside the stomach with an external handheld magnet demonstrated better diagnostic yield and patient tolerance than OGD. Chapter 6: A prospective cohort study of 33 patients with suspected acute upper gastrointestinal bleeding. MACE had higher diagnostic yield for focal lesions and identified additional small bowel bleeding compared to OGD and correctly predicted safe discharge for patients. Chapter 7: A prospective cohort study of 50 patients undergoing examination with the novel upper GI capsule and following a nurse–led series of positional changes to move the capsule around the stomach. The upper GI capsule achieved excellent views of the upper GI tract. In conclusion, these results suggest diagnostic OGD has limitations and upper GI capsule endoscopy has potential as a non-invasive alternative to OGD. These findings are sufficient to reject the null hypothesis.