Each country (or, in the case of Europe, a group of countries) has a corresponding interest rate, it is determined by the central bank. Forex traders monitor interest rates very carefully, because they have a huge impact on currency exchange rates.
European Union: European Central Bank (ECB)
United Kingdom: Bank of England (BoE)
United States: Federal Reserve System (Fed)
Japan: Bank of Japan (BoJ)
Switzerland: Swiss National Bank (SNB)
Canada: Bank of Canada (BoC)
Australia: Reserve Bank of Australia (RBA, RBA)
New Zealand: Reserve Bank of New Zealand (RBNZ, RBNZ)
These central banks raise their interest rates to combat inflation, and also lower them in order to stimulate economic growth. Their actions create fluctuations in exchange rates, which are important in many strategies in the Forex market.