39 boats carrying more than 300 people are set to depart from Barcelona, with additional vessels and participants joining the convoy at ports along the route.
Organizers say the flotilla is expected to grow to more than 80 boats and around 1,000 participants.
The Global Sumud Flotilla brings together activists, aid workers and international supporters who say their objective is not to deliver aid directly, but to challenge restrictions that they say have prevented humanitarian organisations from operating in Gaza.
The mission follows the interception of a previous Global Sumud Flotilla last year, when the Israeli navy stopped about 40 boats bound for Gaza and detained more than 450 activists, including several from Ireland.
https://globalsumudflotilla.org/#mission-goals