The Tibetan Freedom concerts are held to raise money for the Milarepa Fund, an organisation founded by the Beastie Boys supporting non-violent actions to end the Chinese occupation of Tibet. Their website can be found @ milarepa.org
"The Milarepa Fund is an international organization that supports the Tibetan people's nonviolent struggle to regain their freedom. Through grassroots activism, direct action and events such as the Tibetan Freedom Concerts, we actively seek an end to the Chinese government's occupation of Tibet."
Previous events have raised over $2m for the cause. If you wish to know more about what is being fought for, disinfo.com has a brillant introduction here.