The AFC Cup is an annual international club competition between club sides under the Asian Football Federation Confederation (AFC). Qualification to the competition is to clubs from AFC-affiliated countries that fall into the AFC's 'developing nations' category as laid out in their 'Vision Asia' document.
These 'developing nations' are the fourteen 'next-best' countries which lie outside the top-14 countries in the AFC region which send their club sides to the more prestigious Asian Champions League.
Each country sends two teams representing the domestic league winners and the cup winners. The participating teams are split into six groups of three or four, with each team playing the others in the group in a round robin format. The winners of each group and two best runner-ups enter the quarter-finals.
The quarter-finals, semi-finals and finals are played over two legs.
In 2004, Geylang United and Home United both reached the last four of the competition, before they were knocked out by Syrian opposition. This remains the best showing by any S.League side(s) in the history of the AFC Cup.