Tajiks and Iranians have been connected historically and culturally for thousands of years. Tajiks, like the majority of Iranians, are an Iranian people and speak the Persian language, which is also the official language of Iran. Tajikistan, due to historical and cultural ties with Iran and the former Iranian empires, is regarded as a part of Greater Iran.
Iran was one of the first countries to extend diplomatic recognition of the newly independent Tajikistan in 1991 and the first nation to establish an embassy in Dushanbe. Iran provided diplomatic assistance and built new mosques within Tajikistan. Due to the resurgence of Iranian culture within Tajikistan, Iran helped encourage cultural exchange through conferences, media, and film festivals. Iranian television programs, magazines, and books became increasingly common in Tajikistan.
However, despite the many things the nations have in common, there are also vast differences. Tajikistan's post communist government is secular while Iran's is Islamic. Furthermore, Iran is a predominantly Shia nation while Tajikistan is Sunni. The leading figures of the Islamic revival movement in Tajikistan have stated that Iran would not be a model for whatever Islamic government they advocate for Tajikistan.
During the civil war in Tajikistan, Iran offered to mediate between the two factions, however, these efforts did not produce any negotiations. In 1995, Tajikistan opened its first embassy in Tehran, one of the few outside of the former USSR. Relations have since grown stronger, as the two nations cooperate together in the energy sector and officials from both nations have supported stronger ties.
President Ahmadinejad of Iran has commented that "Iran and Tajikistan are one spirit in two bodies". He also added that there are no limits to the expansion of relations between the two countries and that "We do not feel that we have a non-Iranian guest with us thanks to the many commonalities our two countries share".
Iran is the second largest investor in Tajikistan after China. The Iranians built the Sangtuda 2 Hydroelectric Power Plant and Istiklol tunnel in Tajikistan. Preparations are under way for construction of the Shurabad Hydroelectric Power Plant as well as some smaller hydroelectric power plants. Iranian might also participate in the Rogun project (construction of the largest hydroelectric power plant in the region). Iranian specialists built highways and railroads that will connect Tajikistan, Afghanistan and Iran.