The <div> tag is used to designate a block-line portion of an HTML document as a div element and to apply any of the core attributes of this tag against the contents of that element. The behavior of this tag is block-line, because this tag causes a line break (the equivalent of a br tag) to occur both before and after the div element. div tags, which can be nested, allow a significant degree of control and manipulation of each individual block section of your web page.