A tariff is a tax on imports. An import quota is a limit on the quantity of a good that may be imported over a specified period. Both are forms of protectionism: measures that restrict international trade, often to support domestic producers.

How do they work?

A tariff makes imported goods more expensive to bring into a country. If some of that cost is passed on to buyers, the price they pay rises and they may buy fewer imports. The government receives tax revenue on the goods that are imported.

A quota restricts how many units can be imported. If the limit is binding—meaning importers would otherwise bring in more—the reduced supply can push up the domestic price. A quota does not automatically give the government tax revenue. Instead, the right to import within the quota can become valuable; who gains depends on how those rights are allocated.

A tariff does not impose a quantity limit: imports can continue if buyers are willing to pay the higher price. By contrast, once a binding quota is filled, further imports are prohibited for that period. The effect of either policy on consumer prices depends on market conditions.

For example, suppose a country imports bicycles. A tariff of $10%10\%$ taxes each imported bicycle, but does not set a maximum number. A quota of $1{,}000$ bicycles permits no more than that number during the stated period, but does not itself tax them.

The key exam distinction: a tariff changes the cost of importing, while a quota sets a quantity limit. Do not say that both always reduce imports by a fixed amount. Imports can still rise under a tariff if demand grows; a quota only constrains imports when its limit is binding.

This covers tariffs and import quotas within the AS Level topic Protectionism ( $6.2.2$ ); that point also includes other tools of protection.