Forex is the one financial market that never sleeps, meaning you can trade at all hours of the day (or night). Unlike the world's stock exchanges, which are located in physical trading rooms like the New York Stock Exchange or the London Stock Exchange, the Forex market is known as an 'Over-the-counter market' (or OTC). This means that the trades take place directly between the parties holding the currencies, rather than being managed via an exchange.
Consequently, the Forex market has never been restricted to the business hours of any one exchange.
However, since the Forex market is a global market, it means there is always a part of the world that is awake and conducting business, and during these hours their currencies tend to experience the most movement. For example, currency pairs involving the US dollar experience the most movement during US business hours (16:00 to 24:00 GMT), while the Euro, Pound, Swiss Franc, and other European currencies experience the most movement during European business hours, (8:00 and 16:00 GMT).
By contrast, the Australian Dollar, the New Zealand Dollar and the Japanese Yen tend to be more active between 00:00 and 08:00 GMT. As a trader, this means you can trade whenever it suits you - if you work during the day, there will be currencies available to trade before or after work. If you have children but are at home during the day, you can simply choose a different currency. In the Forex market, you can trade 24 hours a day, 5 days a week.