Vasculitis is inflammation of blood vessels that can affect single or multiple organ systems. It is classified based on the size of vessels involved. Diagnosis involves clinical features, lab tests like ESR, and biopsy. Treatment depends on type but often involves steroids. Giant cell arteritis and Takayasu arteritis specifically involve medium and large vessels. Giant cell arteritis commonly affects the temporal artery and presents with headaches. Both require long term steroids to prevent complications.