Subclavian steal syndrome is characterised haemodynamically by severe stenosis between the subclavian artery and the origin of the vertebral artery, leading to low blood pressure in the post-stenotic segment of the subclavian artery. As a result, blood from both the contralateral vertebral artery and the basilar artery flows towards the ipsilateral vertebral artery, away from the brain stem. This situation may cause symptoms of vertebrobasilar and upper extremity ischaemia. The prevalence of subclavian steal syndrome is not well defined, due to the generally asymptomatic nature of the disease. Many patients do not require invasive evaluation or treatment. However, medical, surgical or endovascular treatments should be performed for symptomatic patients. In this chapter, the aetiology, physiopathology, diagnosis and treatment of subclavian steal syndrome will be discussed.