Membership of WWOOF UK enables you to volunteer with hosts in England, Scotland, Wales and Northern Ireland only.
There are WWOOF national organisations in many other countries. For example, joining WWOOF Portugal allows you to WWOOF in Portugal. There is currently no international membership - you must join the national WWOOF organisation in each country where you want to WWOOF. The membership fees are small and cover the cost of running each service. See wwoof.net
For countries where no national organisation exists, host lists are held by WWOOF Independents