National Income is the total value of goods and services produced by a nation in a given period. Definition: Sum of all final goods and services produced within national borders, measured at current prices. Related concepts: GDP (Gross Domestic Product)—production within borders, irrespective of ownership. GNP (Gross National Product)—production by nationals, regardless of location. NDP (Net Domestic Product)—GDP minus depreciation. NNP (Net National Product)—GNP minus depreciation. Per capita income: National income divided by population, indicating average living standards. Income methods: Income approach (sum of factor incomes: wages, rent, interest, profit), Expenditure approach (consumption + investment + government spending + net exports), Output approach (sum of value added by sectors). Measures wealth creation, development level, living standards. Indian context: India's national income measured by Central Statistics Office; NITI Aayog tracks development metrics. ICAI focus: Definitions, calculating national income, distinguishing concepts. Exam tip: Remember GDP vs. GNP distinction; GDP is produced within borders (territorial), GNP is produced by nationals (citizenship-based).