Obesity is becoming a global concern because many non-communicable diseases are attributable to obesity. Though it is highly prevalent in developed countries, obesity is quickly growing to be of concern in low- and middle-income countries such as Thailand, primarily due to the potential strain on its limited resources. Given the potential effect of obesity on the Thai health system, this paper discusses the trends, causes, and impact of obesity in Thailand. It is particularly geared for similar settings that will be dealing with this issue in coming decades. Based on a review of existing and grey literature, this paper addresses the following topics. The epidemiology of obesity in Thailand is described to provide an understanding of the overall trends of its prevalence in terms of sex, age, and geographical location. The etiology of obesity explores its causes and risk factors for children, adults, and the elderly. Obesity's impact is outlined in terms of the health and non-health impacts of obesity, including the health problems resulting from this condition, the cost to the healthcare system of obesity-related illnesses, and the social impact of obesity. The general framework for economic cost estimation of obesity is also illustrated for readers without economic background to better understand the approach. This paper concludes with the policy responses of the government and provides an idea of the various ways that the country has tackled this issue.