Yemen's security forces have carried out hundreds of arbitrary arrests and dozens of enforced disappearances of civilians in the context of its armed conflict with rebels known as Huthis in the northern governorate of Sa'da. The Huthis, named after their original leader, took up arms in 2004 when the government closed their Zaidi Shi'a religious schools. Among those detained were family members held as hostages, others apparently arrested for their religious activism, and civilians held on suspicion of sympathizing with the Huthis. Since 2007, the authorities have also targeted people who published critical news about the conflict. Following a ceasefire in July 2008, Yemeni President Ali Abdullah Saleh announced the release of some Zaidi prisoners, but an unknown number remain detained and new arrests have taken place. This report documents the ease and impunity with which security forces arbitrarily arrest and sometimes "disappear" persons. In nearly all cases, officials did not identify themselves or inform the detainee or his family why or where he was being taken. Most detainees, when they reappeared, have done so at the Political Security Organization, the domestic intelligence agency linked to the president's office. The report calls for independent investigations into human rights violations and the prosecution of those responsible -- and for the Yemeni government to take immediate measures to end the practice of enforced disappearances, to release all persons arbitrarily arrested and detained, and to promptly try persons charged with a cognizable criminal offense in a fair trial meeting international standards.