Systemic hypertension is increasingly recognized within the canine and feline population, particularly in older patients. Blood pressure (BP) is the product of cardiac output and total peripheral resistance, and cardiac output in turn is determined by the heart rate and stroke volume. In health, the baroreceptor reflex interacts with the autonomic nervous system and both local and systemic vasoactive agents to regulate the heart, peripheral vasculature and the renin-angiotensin-aldosterone system (RAAS), keeping BP tightly controlled. Systemic vascular resistance is maintained partly through peripheral vascular compliance and elasticity, particularly of the arteriolar beds. This chapter looks at Target organ damage; Classification of systolic hypertension; Indications for measuring blood pressure; Diagnosis of systemic hypertension; and Treatment and management of systemic hypertension.