Ethnicity touches nearly every aspect of social and cultural life. Anthropologists, sociologists, psychologists, economists, historians, political scientists, literary figures, politicians, lawyers, and even bankers all share a lively interest in the topic. It is hardly surprising that the major concepts involving the notion of "ethnic" differences are essentially meaningless without careful definition. There is, in fact, scarcely a common core meaning in the ways various interested parties uses the notion of "ethnic" except that it refers to an important (or potentially important) difference between different kinds of people. The importance of the difference almost always has something to do with distribution of resources. This chapter addresses these core ideas in the study of ethnic relations with particular reference to social and economic over the past ten years in a village of Mon traders in Thailand.