Major theoretical models of migration and the hypotheses derived from them as well as previous research on migration in Thailand are reviewed as background for a discussion of the methodology and results of this study of migration flows between provinces (changwats) in Thailand. The analysis differs from previous studies in that it includes all nonzero inter-changwat migration streams in the analysis, examines all changwats together and includes separate analyses for Bangkok and non-Bangkok migration; analyzes female and male migration streams separately and also pools the data; includes interaction effects in the equations; tests relative and expanded gravity models which assume respectively that only the characteristics of the destination relative to the origin are important or that characteristics of origin and destination can be examined separately; and measures some key variables in a different way. The data were obtained primarily from the 1970 population census. The economic variables included in the analysis were chosen for relevance to the Thai context and therefore include rural to rural migration; the availability of farmland was added to the standard economic variables of income and unemployment, and the proportions of population living in urban areas was added to test the city lights hypothesis. The multivariate analysis indicated among other findings that economic factors predominate over the noneconomic attributes of urban areas; the economic conditions in destinations relative to origins have significant relationships in the hypothesized direction; male and female migration streams respond to per capita income and unemployment in the same way but males are more responsive to the availability of farmland; migration to and from Bangkok responds similarly to relative income and the availability of farmland as migration to and from other areas; in the unconstrained model, conditions in the area of destination all have significant relationships of the hypothesized signs; conditions in the area of origin play a more complex role, since they determine the push to migrate and also the ability to migrate; and the sign and significance of other economic variables at the origin vary depending on the specifications. The main conclusion of policy relevance is that the level of migration will increase with economic development, but the direction of movement will depend on the relative economic opportunities in various changwats, which may in turn be most susceptible to policy manipulation.