The availability of computerized devices with different screen sizes and different capabilities, and the need to deliver a website on as many of them as possible has led to the invention of various types of solutions. These solutions include designing a fixed- structure layout for a specific class of screen sizes and capability, designing a fluid layout that changes size according to screen size, and designing responsive or adaptive layouts that resize and reorganize their components to suit a user’s device. This chapter discusses these layout design approaches and how they are implemented, especially through CSS flexible box and CSS grid layout properties.