Public Expenditure is government spending on goods, services, and transfers to achieve policy objectives. Classification by nature: Consumption expenditure (salaries, supplies, current operations), Investment expenditure (infrastructure, long-term assets), Transfer payments (pensions, subsidies, welfare, no goods/services received in return). Classification by function: Defense and security, Education and health, Infrastructure and development, Interest on public debt, Welfare and social security, Administrative costs. Productive vs. unproductive: Productive spending (education, infrastructure) yields future returns and economic growth; Unproductive spending (defense, subsidies) immediate costs without direct production benefit (debated). Mandatory vs. discretionary: Mandatory (constitutionally required, debt interest), Discretionary (annual budgeting decisions). Trends: Developed countries spend more on welfare; developing countries on infrastructure and basic services; debt servicing increases share over time. Crowding out: Excessive government spending raises interest rates, reducing private investment. Multiplier effects: Government spending creates income multiplier effects, stimulating economy. Indian context: Spending on MGNREGA, education, health, infrastructure; interest payments increasing share. ICAI focus: Expenditure classification, effects on economy, sustainability. Exam tip: Transfer payments don't directly create goods but redistribute income; inclusion in national income calculations requires care.