The HTML id attribute is a way to identify elements; they have to be unique for each element, unlike classes. To define them, you can use the ID global attribute of the HTML elements, and as the name specifies, an id cannot repeat. The purpose of IDs is when linking to an element, you can easily reference them in scripting or styling. You can access these IDS by adding a “#” before the id name. It is a valuable way to manipulate each unique element instead of accessing a group of elements.