When the internet was first introduced, all websites were written in HTML. HTML was the only programming language used to describe and display data on the World Wide Web. It was simple and fairly easy to learn. As time progressed, programmers started to realize that they were being stymied by HTML. Web designers wanted to be able to describe data more effectively. This need for a better way to deal with data resulted in the development of a new specification called XML. What is XML? XML stands for Extensible Markup Language. So, just like HTML, XML is a markup language. A markup language is any language that is used to describe or define information and text. XML is not a substitute for HTML. It is to be used in conjunction with HTML. HTML focuses on describing how data or text is supposed to be displayed. The XML language does something totally different. XML describes what the data is. So, XML is not something that is apparent on a web page, because it does not actually do anything. As information and data presented on the World Wide Web became more complex, XML was invented to effectively structure, store, and send this information. What makes XML truly unique is that there are no predefined tags like we have with HTML. All of the tags used in HTML have already been defined, such as the paragraph tag, the header tag, and all the various style tags. XML is not defined. You can make your own tags! So, the question is, why do we need XML? Why do we need a more versatile specification like XML to describe data? After all, HTML works fine if used properly, so why do we need XML? Well, the answer is simple. XML is a device independent, cross-platform language. This is extremely important, because people are now using a wide variety of gadgets to connect to the internet, as almost every electronic device on the market now comes equipped with email and internet access. Cell phones, palm tops, computers installed in automobiles, they all have built-in web access. Each of these devices display text and graphics differently, and utilize different platforms and a variety of web browsers. As a result, someone using a cell phone to access a certain web site may not be able to view the data on that website properly because the browser running on that cell phone might not be able to properly display the HTML. The platforms that run on some of these newfangled products and devices are simply not 100% compatible with HTML. XML solves this problem by making sure that the most important data on your website can be displayed across all of these different platforms. This is what makes XML so valuable. The other important features of XML is that it enables data to be exchanged between incompatible systems, and because XML files are plain text files, basically anyone using any system can view the contents of the text file. So, if you are a programmer, you need to learn to use XML for describing, storing, and sending data on the web. With so many different means available to connect to the internet, you should learn to use programming languages like XML.