Tag clouds are everywhere on the web these days. First popularized by the web sites Flickr, Technorati, and del.icio.us, these amorphous clumps of words now appear on a slew of web sites as visual evidence of their membership in the elite corps of "Web 2.0." This PDF analyzes what is and isn't a tag cloud, offers design tips for using them effectively, and then goes on to show how to collect tags and display them in the tag cloud format. Scripts are provided in Perl and PHP. Yes, some have said tag clouds are a fad. But as you will see, tag clouds, when used properly, have real merits. More importantly, the skills you learn in making your own tag clouds enable you to make other interesting kinds of interfaces that will outlast the mercurial fads of this year or the next.