Contact angle is one of the common ways to measure the wettability of a surface or material. Wetting refers to the study of how a liquid deposited on a solid (or liquid) substrate spreads out. There are a variety of techniques used to measure contact angle; among these techniques, the recently developed methods known as droplet-shape analysis have attracted a lot of attentions. Contact angle measurement using sessile drop technique is a droplet-shape analysis method.

The sessile drop contact angle is measured by a contact angle goniometer using an optical subsystem to capture the profile of a pure liquid on a solid substrate. Older systems used a microscope optical system with a back light. Current-generation systems employ high resolution cameras and software to capture and analyze the contact angle.