During the nineteenth century, as today, nausea and vomiting were common signs and symptoms of illness, the interpretation of which contributed to doctors' diagnostic, prognostic and therapeutic choices. At the core of this thesis lies the research question: how did medical understandings and management of nausea and vomiting change in the period 1800-1900? In addition to being signs of bodily disorder, nausea and vomiting constituted an individual, typically non-medicalised experience of sickness. As such, a secondary thesis question is: how were nausea and vomiting experienced, interpreted and responded to by sufferers? These questions are pursued through four key themes: physiology, vomit analysis, morning sickness and sea-sickness. Medical textbooks, journals, hospital case reports, newspapers, letters and diaries are the principal source base.Throughout the nineteenth century physiological explanations for nausea and vomiting followed a generally reductionist path. In the 1830s Marshall Hall's reflex theory encouraged new perceptions of the nervous mechanisms involved in nausea and vomiting, and helped stimulate their redefinition into local, central and peripheral causes. Changing physiological explanations for nausea and vomiting were also contemporaneous to the growth of microscopy. This thesis draws attention to the interest nineteenth-century practitioners showed in using vomited matters as pathological fluids. This is explored primarily through a case study of sarcina ventriculi, a vegetable microorganism discovered in fermenting vomit. Responses to this discovery showed that laboratory techniques were largely inapplicable to everyday occurrences of nausea and vomiting. Consequently, neither the increasing localisation of the causes of vomiting, nor interest in vomited matters as pathological fluids, contributed to specificity in diagnoses or treatments. This research thereby demonstrates the cumulative and overlapping nature of nineteenth-century medical cosmologies - 'bedside', 'hospital' and 'laboratory' - and the continuation of the 'clinical art'.The histories of morning sickness and sea-sickness contextualise medical understandings of nausea and vomiting in relation to these transient conditions. They bring to the fore perceptions of health and sickness and show that medical theory was often secondary to cultural beliefs and practices. Specifically, this thesis questions the medicalisation of pregnancy during the nineteenth century and uses experiences of sea-sickness to reveal new features of Victorian understandings of the mind-body relationship. This thesis shows that 'feeling sick' (nausea) was arguably as significant to contemporaries as actually 'being sick' (vomiting). It also confirms the complexity and fluidity of taken-for-granted terms such as: 'patient', 'sufferer', 'disease', 'illness' 'sign' and 'symptom', and, of course, 'sick'. Furthermore, it demonstrates the importance to historians of studying everyday, self-limiting illnesses and morbidity.