Market Drivers of Web 2.0
While the term might have appeared out of nowhere, the underlying fundamentals of this evolutionary shift stay the same:

• Broadband has become mainstream and ubiquitous, resulting in an increased usage of the Internet for even small tasks on different devices.
• More people go online for a variety of tasks and shopping-related activities.
• The founders and executive management of the first batch of companies have moved on - either joined one of the big players, left to join VCs, or start or join a completely new thing. This means a lot of experience of what did and didn't work is in the mix.
• New ventures can grow more slowly - barriers to entry are lower, there's less pressure to gain venture capital, less hype to cater to.

New web-based communities
Web 2.0 has created new online social networks amongst the general public. Some of the websites run social software where people work together. Other websites reproduce several individuals RSS feeds on one page. Other ones provide deeplinking between individual websites.

The syndication and messaging capabilities of Web 2.0 have created, to a greater or lesser degree, a tightly-woven social fabric among individuals that would have formerly been impossible. Unarguably, the nature of web-based communities has changed in recent months and years. The meaning of these changes, however, has pundits divided. Basically, ideological lines run thusly: Web 2.0 either empowers the individual and provides an outlet for the 'voice of the voiceless'; or it elevates the amateur to the detriment of professionalism, expertise and clarity.

New web-based applications
The richer user experience afforded by Ajax has prompted the development of web sites that mimic personal computer applications, such as word processing, the spreadsheet, and slide-show presentation. Wysiwyg wiki sites replicate many features of PC authoring applications. Still other sites perform collaboration and project management functions. Java enables sites that provide compute-intensive video capability. One of the best known sites of this broad class, Writely, was acquired by Google in early 2006.

Critics refer to this trend as ASP 1.1, and point out that numerous similar web-based application services, or ASPs, appeared during the dotcom bubble, and then vanished, having failed to gain a critical mass of customers. The best known of these, Intranets.com was acquired in 2005 by WebEx for slightly more than the total it had raised in venture capital, after six years in business. Whether a large market will embrace a model that requires businesses to hand over both software and data to third parties remains a topic of debate.

Advanced technology
The technology infrastructure of Web 2.0 is complex and evolving; it includes server software, content syndication, messaging protocols, standards-based browsers, and various client applications. (Non-standard browser plugins and enhancements are generally eschewed.) These differing but complementary approaches provide Web 2.0 with information storage, creation, and dissemination capabilities that go beyond what was formerly expected of websites.

Overview of Web 2.0 techniques
A website could be said to be built using Web 2.0 technologies if it features a number of the following techniques:

• Technical
  Unobtrusive Rich Internet Application techniques (such as Ajax)
• CSS
• Semantically valid XHTML markup and/or the use of Microformats
• Advanced User Interface languages such as XUL and SVG
• Flash Remoting
• Syndication of data in RSS/Atom
• Aggregation of RSS/Atom data
• Clean and meaningful URLs
• Weblog publishing
• REST or XML Webservice APIs
• Some social networking aspects

General
The site should not act as a "walled garden" - it should be easy to get data in and out of the system.
Users usually own their data on the site and can modify at their convenience
Mainly web-based - most successful Web 2.0 applications can be used almost entirely through a web browser: this is commonly referred to by the phrase "network as platform".
Applicable to an emerging generation of game development, proposed as thin games
Data returns should be dynamic, not static, changing depending on variables associated with the user's query (e.g. keywords, location).

Rich Internet Applications
Recently, Rich Internet Application techniques such as Ajax have evolved that can improve the user experience in browser-based web applications. Ajax involves a web page requesting an update for some part of its content, and altering that part in the browser, without refreshing the whole page at the same time. There are proprietary implementations (as in Google Maps) and open forms that can utilise web service APIs, syndication feeds, or even screen scraping.

Server-side software
The functionality of Web 2.0 Rich Internet Applications builds on the existing web server architecture, but puts much greater emphasis on back-end software. Syndication differs only nominally from dynamic content management publishing methods, but web services typically require much more robust database and workflow support, and become very similar to the traditional intranet functionality of an application server. Vendor approaches to date fall under either a universal server approach, which bundles most of the necessary functionality in a single server platform, or a web server plugin approach, which uses standard publishing tools enhanced with API interfaces and other tools. Regardless of the approach chosen, the evolutionary path toward Web 2.0 is not expected to be significantly altered by these choices.

Client-side software
The extra functionality provided by Web 2.0 depends on users having more than passive access to the data on the servers. This can be through forms in an HTML page, a scripting language such as Javascript, or through Java. These methods all make use of the client computer to take varying degrees of work off the server.

RSS
The first and most important evolution towards Web 2.0 involves the syndication of website content, using standardized protocols which permit end-users to make use of a site's data in another context, ranging from another website, to a browser plugin, or a separate desktop application. Protocols which permit syndication include RSS, RDF (as in RSS 1.1), and Atom, all of which are flavors of XML. Specialized protocols such as FOAF and XFN (both for social networking) extend functionality of sites or permit end-users to interact without centralized websites. See microformats for more specialized data formats.

Due to the recent development of these trends, many of these protocols remain de facto rather than formal standards.

Web protocols
Web communication protocols are a key element of the Web 2.0 infrastructure. Two major ones are REST and SOAP. More recently, SOAP has dropped the acronym and is now only known as SOAP.

• REST (Representational State Transfer) indicates a way to access and manipulate data on a server using the HTTP verbs GET, POST, PUT, and DELETE.
• SOAP involves POSTing XML messages and requests to a server that may contain quite complex, but pre-defined, instructions for it to follow.

In both cases, access to the service is defined by an API. Often this API is specific to the server, but standard web service APIs (for example, for posting to a blog) are also widely used. Most, but not all, communications with web services involve some form of XML (Extensible Markup Language).

See also WSDL (Web Services Description Language), which is the standard way of publishing a SOAP API, and the list of Web service specifications for links to many other web service standards, including those many whose names begin 'WS-'.

Criticism
As there are no set standards for what Web 2.0 actually means, implies, or requires, the term can mean radically different things to different people. For instance, many people pushing Web 2.0 talk about well-formed, validated HTML; however, not many production sites actually adhere to this standard. Many people will also talk about web sites "degrading gracefully" (designing a website so that its fundamental features are still useable by people who are accessing it with software that does not support every technology employed by the site); however, the addition of Ajax scripting to websites will often render the website completely unusable to anyone browsing with JavaScript turned off, or using a slightly older browser. Many have complained that the proliferation of Ajax scripts, along with unknowledgeable webmasters, has increased the instances of "tag soup": websites where <script> tags, and other semantically useless tags, are thrown about the HTML file with little organization in mind, in a way that was more commonly done during the dot-com boom, and is something many standards proponents have been trying to move away from.

Many of the ideas of Web 2.0 have been employed on websites that were around well before the term was developed; Amazon.com, for instance, has allowed users to write reviews and consumer guides since its inception, in a form of self-publishing, and opened up its API to outside developers in 2002. [3] Conversely, when a website proclaims itself Web 2.0 for the use of some trivial feature such as blogs or gradient boxes, it is generally more of an attempt at self-promotion than an actual endorsement of the ideas behind Web 2.0. It has sometimes been reduced to simply a marketing buzzword, like 'synergy', that can mean whatever a salesperson wants it to do, with little connection to most of the good, but unrelated ideas that it is based on. It could also be argued that "Web 2.0" does not represent a new version of World Wide Web at all, and is in fact comprised entirely of "Web 1.0" technologies and concepts.

Other criticism has included the term "a second bubble" stating that there are too many Web 2.0 companies attempting to create the same product with a lack of business models.