LinkedIn(pron.ˌlɪŋkt.ˈɪn)is a social networking website for people in professional occupations.Founded in December 2002 and launched on May 5,2003,it is mainly used for professional networking.As of January 2013,LinkedIn reports more than 200 million acquired users in more than 200 countries and territories.

The site is available in English,French,German,Italian,Portuguese,Spanish,Dutch,Swedish,Romanian,Russian,Turkish,Japanese,Czech,Polish,Korean,Indonesian,and Malay.Quantcast reports LinkedIn has 21.4 million monthly unique U.S.visitors and 47.6 million globally.In June 2011,LinkedIn had 33.9 million unique visitors,up 63 percent from a year earlier and surpassing MySpace.LinkedIn filed for an initial public offering in January 2011 and traded its first shares on May 19,2011,under the NYSE symbol LNKD.

LinkedIn's CEO is Jeff Weiner,previously a Yahoo!Inc.executive.The company was founded by Reid Hoffman and founding team members from PayPal and Socialnet.com(Allen Blue,Eric Ly,Jean-Luc Vaillant,Lee Hower,Konstantin Guericke,Stephen Beitzel,David Eves,Ian McNish,Yan Pujante,and Chris Saccheri).

Founder Reid Hoffman,previously CEO of LinkedIn,is now Chairman of the Board.Deep Nishar is Vice President of Products.LinkedIn is headquartered in Mountain View,California,with offices in Omaha,Chicago,New York,London and Dublin.It is funded by Sequoia Capital,Greylock,Bain Capital Ventures,Bessemer Venture Partners and the European Founders Fund.LinkedIn reached profitability in March 2006.Through January 2011,the company had received a total of$103 million of investment.

In late 2003,Sequoia Capital led the Series A investment in the company.In June 2008,Sequoia Capital,Greylock Partners,and other venture capital firms purchased a 5%stake in the company for$53 million,giving the company a post-money valuation of approximately$1 billion.

In 2010,LinkedIn opened a European headquarters in Dublin,Ireland,received a$20 million investment from Tiger Global Management LLC at a valuation of approximately$2 billion,and announced its first acquisition,Mspoke,and improved its 1%premium subscription ratio.In October of that year Silicon Valley Insider ranked the company No.10 on its Top 100 List of most valuable start ups.By December,the company was valued at$1.575 billion in private markets.

LinkedIn filed for an initial public offering in January 2011 and traded its first shares on May 19,2011,under the NYSE symbol LNKD,price of IPO was$45 per share.Shares of LinkedIn,which rose as much as 171 percent in their first day of trade on the New York Stock Exchange,closed at$94.25,more than 109 percent above IPO price.

In 2011,LinkedIn earned$154.6 million in advertising revenue alone,surpassing Twitter which earned$139.5 million dollars.LinkedIn’s fourth-quarter 2011 earnings soared due to the company's increase in success in the social media world.

In the spring of 2012,LinkedIn expanded its office space by 57,120 square feet in the Financial District of San Francisco.In May 2012,LinkedIn announced its 2012 Q1 revenues were up 101%to$188.5 million compared to$93.9 million in Q1 of 2011,with net income increasing 140%over Q1'2011 to$5 million.Revenue for Q2 was estimated to be between$210 to$215 million.

In June 2012 cryptographic hashes of approximately 6.4 million LinkedIn user passwords were stolen by hackers who then published the stolen hashes online.In response to the incident,LinkedIn asked its users to change their passwords.Security experts criticized LinkedIn for not salting their password file,and instead using a single iteration of SHA-1.

In November 2012,LinkedIn released their third quarter earnings,reporting earnings-per-share of$0.22 on revenue of$252 million.In result of these numbers,LinkedIn's stock was up,trading at roughly$112 a share.

LinkedIn has more than 200 million members in over 200 countries and territories.It is significantly ahead of its competitors Viadeo(50 million)and XING(10 million).The membership grows by approximately two new members every second.About half of the members are in the United States and 11 million are from Europe.With 3 million users,India has the fastest-growing network of users as of 2009.The Netherlands has the highest adoption rate per capita outside the US at 30%.LinkedIn recently reached 4 million users in UK,1 million in Spain,and nearly 1 million in Pakistan.

As of March 2011 the service had 44 million users in the US and 56 million outside.As of October 2011,LinkedIn has over 14 million students and recent college graduates as members.In November 2012,LinkedIn announced it had 187 million members.LinkedIn grew by 10 to 15 million members per quarter throughout 2012.

One purpose of the site is to allow registered users to maintain a list of contact details of people with whom they have some level of relationship,called Connections.Users can invite anyone(whether a site user or not)to become a connection.However,if the invitee selects I don't know or Spam,this counts against the inviter.If the inviter gets too many of such responses,the account may be restricted or closed.

This list of connections can then be used in a number of ways
A contact network is built up consisting of their direct connections,the connections of each of their connections(termed second-degree connections)and also the connections of second-degree connections(termed third-degree connections).This can be used to gain an introduction to someone a person wishes to know through a mutual contact.

Users can upload their resume or design their own profile in order to showcase work and community experiences.

It can then be used to find jobs,people and business opportunities recommended by someone in one's contact network.

Employers can list jobs and search for potential candidates.

Job seekers can review the profile of hiring managers and discover which of their existing contacts can introduce them.

Users can post their own photos and view photos of others to aid in identification.

Users can now follow different companies and can get notification about the new joining and offers available.

Users can save(i.e.bookmark)jobs that they would like to apply for.

The gated-access approach(where contact with any professional requires either an existing relationship,or the intervention of a contact of theirs)is intended to build trust among the service's users.LinkedIn participates in the EU's International Safe Harbor Privacy Principles.

The feature LinkedIn Answers,similar to Yahoo!Answers,allowed users to ask questions for the community to answer.This feature was free,and the main difference from the latter was that questions are potentially more business-oriented,and the identity of the people asking and answering questions is known.As of January 31,2013,the LinkedIn Answers feature is no longer supported.LinkedIn cites a new'focus on development of new and more engaging ways to share and discuss professional topics across LinkedIn.'as the reason for the retirement of the feature.

Another LinkedIn feature is LinkedIn Polls.In December 2011,LinkedIn announced that they are rolling out polls to their one million groups.

In mid-2008,LinkedIn launched LinkedIn DirectAds as a form of sponsored advertising.

In October 2008,LinkedIn revealed plans to open its social network of 30 million professionals globally as a potential sample for business-to-business research.It is testing a potential social-network revenue model-research that to some appears more promising than advertising.

Applications
In October 2008,LinkedIn enabled an applications platform that allows other online services to be embedded within a member's profile page.Among the initial applications were an Amazon Reading List that allows LinkedIn members to display books they are reading,a connection to Tripit,and a Six Apart,WordPress and TypePad application that allows members to display their latest blog postings within their LinkedIn profile.

In November 2010,LinkedIn allowed businesses to list products and services on company profile pages;it also permitted LinkedIn members to recommend products and services and write reviews.

Mobile
A mobile version of the site was launched in February 2008,which gives access to a reduced feature set over a mobile phone.The mobile service is available in six languages Chinese,English,French,German,Japanese and Spanish.

In January 2011,LinkedIn acquired CardMunch,a mobile app maker that scans business cards and converts into contacts.LinkedIn plans to integrate this functionality into their services in the near future.In August 2011,LinkedIn revamped its mobile applications on the iPhone,Android and HTML5.Mobile page views of the application have increased roughly 400%year over year according to CEO Jeff Weiner.

Groups
LinkedIn also supports the formation of interest groups,and as of March 29,2012 there are 1,248,019 such groups whose membership varies from 1 to 744,662.The majority of the largest groups are employment related,although a very wide range of topics are covered mainly around professional and career issues,and there are currently 128,000 groups for both academic and corporate alumni.

Groups support a limited form of discussion area,moderated by the group owners and managers.Since groups offer the ability to reach a wide audience without so easily falling foul of anti-spam solutions,there is a constant stream of spam postings,and there now exist a range of firms who offer a spamming service for this very purpose.LinkedIn has devised a few mechanisms to reduce the volume of spam,but recently took the decision to remove the ability of group owners to inspect the email address of new members in order to determine if they were spammers.Groups also keep their members informed through emails with updates to the group,including most talked about discussions within your professional circles.

Groups may be private,accessible to members only or may be open to Internet users in general to read,though they must join in order to post messages.