A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, wetting has been studied using contact angles of drops on solids for more than 200 years, the question remains unanswered: Is wetting of a rough and chemically heterogeneous surface controlled by the interactions within the solid/liquid contact area beneath the droplet or only at the three-phase contact line? After the publications of Pease in 1945, Extrand in 1997, 2003 and Gao and McCarthy in 2007 and 2009, it was proposed that advancing, receding contact angles, and contact angle hysteresis of rough and chemically heterogeneous surfaces are determined by interactions of the liquid and the solid at the three-phase contact line alone and the interfacial area within the contact perimeter is irrelevant. As a consequence of this statement, the well-known Wenzel (1934) and Cassie (1945) equations which were derived using the contact area approach are proposed to be invalid and should be abandoned. A hot debate started in the field of surface science after 2007, between the three-phase contact line and interfacial contact area approach defenders. This paper presents a review of the published articles on contact angles and summarizes the views of the both sides. After presenting a brief history of the contact angles and their measurement methods, we discussed the basic contact angle theory and applications of contact angles on the characterization of flat, rough and micropatterned superhydrophobic surfaces. The weak and strong sides of both three-phase contact line and contact area approaches were discussed in detail and some practical conclusions were drawn.

固着液滴是一种独立的液滴，已经沉积在固体基材上，其中的润湿区域受到三相接触线的限制，并具有接触角，接触半径和液滴高度的特征。尽管已经使用液滴在固体上的接触角进行了200多年的研究，但问题仍未得到解决：是通过液滴下方或仅在液滴下方的固/液接触区域内的相互作用来控制粗糙且化学不均一的表面的润湿三相接触线？在1945年的Pease，1997年，2003年的Extrand以及2007年和2009年的Gao和McCarthy出版之后，提出了前进，后退的接触角，粗糙和化学非均质表面的接触角滞后由单独的三相接触线上的液体和固体相互作用决定，接触周界内的界面面积无关紧要。由于这种说法，使用接触面积法推导的著名的Wenzel（1934）和Cassie（1945）方程被认为是无效的，应该放弃。2007年之后，在三相接触线和界面接触区域进近防御者之间，开始在表面科学领域引起了激烈的争论。本文介绍了有关接触角的已发表文章，并总结了双方的观点。在简要介绍了接触角及其测量方法的历史之后，我们讨论了基本接触角理论和接触角在平坦，粗糙和微图案超疏水表面表征上的应用。详细讨论了三相接触线和接触区域方法的弱侧和强侧，并得出了一些实用的结论。