Web application development is the creation and maintenance of software applications to be used on the World Wide Web. It is performed by specialized programmers, who are familiar with the coding necessary for the creation of Web pages, including HTML, XML, Flash, Perl, CSS, PHP, JSP, ASP, and others. Each of these has a specific function and creates varied results. Web programmers must be proficient in one or more of these languages to some degree. Development can be varied or specific, depending on the needs of the Web pages involved.

One factor of Web application development that may not be evident to the casual observer is the number of revisions that such applications routinely involve. The World Wide Web is not a strictly controlled environment. People typically use the Web through only one or more of a large handful of methods, primarily Internet browsers. Each Web browser is slightly different and shows pages in slightly different ways. Some are friendlier to certain Web languages than others, and so programming for the Internet can be quite specialized.

A Web programmer must keep this variability in mind when designing sites. Some browsers are certainly more prevalent than others, and many programmers focus on these markets exclusively, figuring that their time will be well spent because their target audience is the majority anyway; however, especially with consumer-based websites, a company never knows where its next high-paying customer is going to come from and what browser he or she will use to try to view the page. Many Web developers design pages using open source code or keep things simple in order to maximize the pages' exposure.

One of the most basic types of Web application development involves e-commerce sites. This is the kind of website that a user sees when he shops online. Designers of these sites must anticipate all kinds of unusual customer behavior, as well as heavy traffic, while keeping the server and "shopping cart" up and running. The ease of online shopping has created an "always-on" environment in which people can shop at all times of the day and night, wherever they are. E-commerce sites must be available to accept orders and money no matter what time it is at corporate headquarters. Development can lend itself specifically to e-commerce site creation, but the programmer would do well to keep the 24/7 mentality of potential customers in mind.

Another kind of Web application development is used for Web-based office applications. Many modern offices use the World Wide Web to conduct their business operations, including all manner of accounting and tracking functions. Conference calls via the Web are also popular, as are file transfers. Developers who work on these types of applications are often in high demand.