Obesity, a widely known risk factor for many chronic diseases, is rapidly increasing in developing countries. Unlike in the developed world, where obesity is largely associated with low socioeconomic status, there is an ongoing debate on whether obesity is a problem of the rich or that of the poor in developing countries. This thesis comprises four studies that seek to improve our understanding of the socioeconomic associations, inequalities in and determinants of obesity in developing countries. In the first study, a systematic review of the literature published between 2004 and 2010 looking at the association between socioeconomic status (SES) and obesity in developing countries was undertaken. This review revealed that in poorer 3 countries obesity is a problem of both men and women with higher socioeconomic status, while it is primarily a problem of women with low SES in middle income countries, implying that the burden of obesity shifts from women with higher SES towards those with lower SES as a country progresses economically. Typically, the burden of obesity switches from women with higher SES to those with lower SES at a Gross National Income per capita of approximately US$1000. This shift is less visible, or takes place more slowly, among men while child obesity is exclusively associated with affluence in developing countries. In the second study, a cross-country analysis was undertaken comparing the Middle East and North African (MENA), a developing region severely affected by obesity, with the rest of the world in order to understand how MENA is different in terms of key socioeconomic determinants of obesity. The cross-country analysis revealed that MENA has seen the biggest increase in calorie supply in the last few decades compared with the rest of the world, and calorie supply is positively associated with obesity in this region. In the third study, an individual-level analysis of more than 800,000 women from 54 low and middle income countries was undertaken to understand individual level factors making women in MENA susceptible to obesity. The individual-level analysis showed that MENA is endowed with obesity risk factors such as the largest number of passenger cars per 1000 people, the highest level of 4 urbanisation, and the highest television viewing frequency compared with other low and middle income countries. In addition, the individual-level analysis revealed that about 80% of MENA women are homemakers (do not participate in the labour force) compared with 50% or less in other developing countries, and being a homemaker is positively associated with obesity in MENA. In the fourth study, the effect of migrating from a developing to developed country was analysed using an innovative treatment group from the UK Understanding Society survey and control groups from the nationally representative Demographic and Health Surveys undertaken in six developing countries (Bangladesh, Ghana, India, Kenya, Nigeria and Uganda). After adjusting for selection bias, this study found that migrating from one of these countries to the UK raised BMI by 1 to 1.6 units for women and 2.5 to 3.2 units for (Indian) men. Likewise, obesity among migrants increased by 3.3 to 5.0 percentage points for women and 3.5 to 6.7 percentage points for Indian men. Analytical information on the emerging problem of obesity in developing countries is crucial for designing intervention programs and policies.