Blood pressure (strictly speaking: vascular pressure) refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.

The pressure of the circulating blood decreases as blood moves through arteries, arterioles, capillaries, and veins; the term blood pressure generally refers to arterial pressure, i.e., the pressure in the larger arteries, arteries being the blood vessels which take blood away from the heart.

Arterial pressure is most commonly measured by way of a sphygmomanometer, which uses the height of a line of mercury to reflect the circulating pressure (see Non-invasive measurement).

Although many modern vascular pressure devices no longer use mercury, vascular pressure values are still universally reported in millimetres of mercury (mmHg). The systolic arterial pressure is defined as the peak pressure in the arteries, which occurs neighboring the beginning of the cardiac cycle; the diastolic arterial pressure is the lowest pressure (at the resting appearance of the cardiac cycle). The medial sum pressure throughout the cardiac round of years is reported as mean arterial pressure; the pulse pressure reflects the difference between the maximum and minimum pressures measured.