The most commonly used programming language for web development is JavaScript. This versatile language enables dynamic content creation, interactive features, and responsive design on the web, making it an essential tool for front-end development. JavaScript works alongside HTML and CSS, allowing developers to create engaging user experiences. Its popularity is further enhanced by numerous libraries and frameworks, such as React, Angular, and Vue.js, which facilitate complex functionalities. Additionally, JavaScript can also be used on the server side through Node.js, expanding its applicability across the entire development stack. Its integration into almost every modern web application solidifies its position in web development.