Many researchers in many territories have carried out studies on the income diversification of households. This paper uses synthesis, evaluation, and analysis methods based on empirical studies regarding income diversification. Based on a synthesis of theories and experimental studies results on income diversification of households in the world and Vietnam, this article presents different definitions of household income diversification from various viewpoints. The research content on income diversification of households is diversified as factors affecting the diversity of income in the push and pull factors, determinants of diversity in income sources, diversification as a commercialization process, diversification towards non-agricultural activities, diversification towards high value-creating activities, and determinants of income diversification in households assets. There are many indicators to measure income diversification. This article also points out the interrelationships between income diversification and households income.