Capital Controls and Convertibility

A currency is fully convertible when anyone, resident or foreign, can exchange it for another currency and move the proceeds across borders without government permission. The US dollar and euro work this way. Many other currencies are only partially convertible: a government may allow convertibility for trade-related payments (importers paying foreign suppliers) while restricting or licensing convertibility for capital movements (foreign investors repatriating profits, residents moving savings abroad).

Capital controls are the tools that enforce this restriction — limits on how much currency an individual or company can convert per year, requirements to get central-bank approval before large transfers, taxes on short-term capital inflows meant to discourage speculative "hot money," or outright bans on certain transactions. Governments use them to protect currency reserves during crises, to slow destabilizing capital flight, or to retain control over monetary policy without an exchange rate that swings freely with global capital flows.

For a trader or investor, capital controls are the reason non-deliverable forwards exist at all: if a currency can't be freely converted and moved offshore, no one outside the country can safely hold or hedge exposure to it through ordinary delivery-based instruments, and cash-settled proxies become the only practical way in.