Encyclopædia Iranica is a project whose goal is to create a comprehensive and authoritative English-language encyclopedia about the history, culture, and civilization of Iranian peoples from prehistory to modern times.

The Encyclopædia Iranica is dedicated to the study of Iranian civilization in the wider Middle East, the Caucasus, Southeastern Europe, Central Asia, and the Indian subcontinent. The academic reference work will eventually cover all aspects of Iranian history and culture as well as all Iranian languages and literatures, facilitating the whole range of Iranian studies research from archeology to political sciences. It is a project founded by Ehsan Yarshater in 1973 and currently carried out at Columbia University's Center for Iranian Studies. It is considered the standard encyclopedia of the academic discipline of Iranistics.

The scope of the encyclopedia goes beyond modern Iran (also known as "Persia") and encompasses the entire Iranian cultural sphere, and far beyond. Relations of the Iranian world with other cultures (China, European countries, etc.) are also covered. The project is planning on publishing a total of up to 45 volumes.

Ehsan Yarshater was the founding editor of Encyclopædia Iranica from 1973 through 2017. The current editor-in-chief is Elton Daniel. The editorial board includes Mohsen Ashtiany, Mahnaz Moazami, and over 40 consulting editors from major international institutions doing research in Iranian studies. Former long tenured editors include Ahmad Ashraf, Christopher Brunner, Habib Borjian, Kioumars Ghereghlou, Manuchehr Kasheff, Dagmar Riedel and Houra Yavari. A growing number (over 1,300 in 2016) of scholars worldwide have contributed articles to Encyclopædia Iranica.

In 1990, Ehsan Yarshater established the Encyclopædia Iranica Foundation (EIF), which serves to promote the cause of the Encyclopædia Iranica and to ensure its continuation. Over the years, Columbia University's Center for Iranian Studies (also founded by Yarshater) continued to coordinate and edit the Encyclopædia, while the EIF substantially sponsored the work.

The foundation provides the full text of many entries (up to fascicle XVI/3) for free on the iranicaonline.org website.

Following Yarshater's retirement as director of the Center for Iranian Studies in 2016, a dispute began to emerge between Columbia University and the EIF as Columbia unilaterally decided to enter into a contract with Brill, an academic publisher, which subsequently published fascicles 4 and 5 of volume XVI in 2018 and 2019; the EIF protested the move. In 2019, Columbia University sued the EIF, seeking, among other things, a finding that the EIF owns neither a copyright nor an exclusive trademark right in the encyclopedia. EIF countersued alleging that Columbia, as well as Brill and Elton Daniel, breached EIF's copyright in the encyclopedia, infringed, diluted, and counterfeited its trademarks, converted EIF property, and committed various acts of unjust enrichment and unfair competition. On July 31, 2020, the U.S. District Court in the Southern District of New York granted a temporary restraining order against Columbia, Brill and Daniel, enjoining them through October 8, 2020 from publishing additional fascicles. EIF also sought a preliminary injunction against the defendants, but such relief was not entered by the court. Columbia and Brill subsequently published fascicle XVI/6 on October 19, 2020.

As part of the dispute, there are now conflicting accounts as to the current state of the Encyclopædia Iranica. While Columbia has published fascicle XVI/4 through XVI/6, covering topics between "Kešaʾi Dialect" and "Khorasan XIV", by EIF's count volume XVI only covers topics falling alphabetically between KA and KE. EIF considers fascicles XVI/4 through XVI/6 "counterfeit fascicles".