Classic FFXI community

Elemental Relationships

Each element has a weakness and a strength.

Fire (Element) > Ice (Element) > Wind (Element) > Earth (Element) > Lightning (Element) > Water (Element) > Fire (Element) ... and keeps going.

Additionally Dark (Element) <--> Light (Element) are opposed elements.

Or, if you like lists:

Fire (Element) melts Ice (Element)
Ice (Element) compacts Wind (Element)
Wind (Element) erodes Earth (Element)
Earth (Element) grounds Lightning (Element)
Lightning (Element) electrifies Water (Element)
Water (Element) douses Fire (Element)
Light (Element) illuminates Dark (Element)
Dark (Element) eclipses Light (Element)

Certain weapon skills have elemental properties, as well.

Ex: Red Lotus Blade > Fire

See also:
Ninja: Elemental Wheel