Yandex (Russian: Я́ндекс) is a Russian search engine and one of the biggest Russian Web portals. It has been online since 1997. Its name can be explained as "Yet A further iNDEXer" (yandex) or "Языково́й (language) Index". The Russian character "Я" corresponds to the English pronoun "I", making "Яndex" a bilingual pun on "Index".

According to research studies conducted by Gallup Media, FOM and Comcon, Yandex is the largest resource and largest search engine in Russian Internet, based on the audience size and internet penetration.

Yandex LLC became profitable in November of 2002. In 2004 Yandex sales increased to $17M, which was 10 times greater than the company revenues just 2 years earlier, in 2002. The net income of the company in 2004 constituted $7M. In June of 2006 the weekly revenue of Yandex.Direct context ads system exceeded $1M. All of Yandex accounting measures have been audited by Deloitte & Touche since 1999.

The closest competitors of Yandex in the Russian market are Rambler and Mail.ru. Although services like Google and Yahoo! are also used by Russian users and have Russian interfaces, Google has about 21-27% of search engines generated traffic to Russian sites and Yandex has around 42-49% (Mar 2007). In Ukraine Yandex enjoys 16 percent share of the search traffic while Google has 40 percent share.

One of the biggest Yandex advantages for Russian-language users is understanding Russian inflection in search queries.

Since 2001, Yandex conducts regular Internet search contests named "Yandex Cup" with several thousands of participants and valuable prizes.

On 6th July 2006, Yandex and the BBC simultaneously hosted a webcast which used viewer's questions to interview Russian President Vladimir Putin. Yandex and the BBC dealt with the Russian-language and the English-language questions respectively. Yandex was represented by Aleksandr Gurnov, a famous Russian journalist and celebrity.

In March 2007 Yandex acquired social networking site Moikrug.ru - - a Russian social network to search and support professional and personal contacts.