Recently one of a beginner stage web designer asked me this question. And my answer is yes, we have to use it. Rel is means Relationship, it is a html attribute which is used to indicate an external style sheet into that web page. Usage sytanx: In the above shown way we have to call an external C S S document. Here Link tag is also an important one, it defines the relationship between a web page html and an external document which is mostly used to call style sheets.