The angle of contact, also known as the contact angle, is the angle formed at the interface between a liquid and a solid surface. It is the angle between the tangent line at the point of contact and the solid surface, as measured through the liquid phase. More specifically, it is the angle between the surface tangent on the liquid–vapor interface and the tangent on the solid–liquid interface at their intersection point. The angle of contact plays a significant role in various scientific and practical applications. It affects phenomena such as adhesion, surface tension, capillary action, and the behavior of droplets on surfaces. Understanding and controlling the angle of contact is crucial in fields such as materials science, surface chemistry, surface coating, and fluid dynamics. The angle of contact can be measured directly by moving drops linearly on a surface and measuring the advancing and receding contact angles. The angle of contact is a crucial parameter that governs the wetting behavior of a liquid on a solid surface. It influences adhesion, surface tension, and capillary phenomena, with wetting angles less than 90 degrees indicating good wetting, angles greater than 90 degrees indicating poor wetting, and angles between 0 and 90 degrees representing partial wetting.