The relations between the Islamic Republic of Iran and Iraq during the period after the Islamic Revolution have transformed from a bloody confrontation in the eight-year war, following the fall of Saddam Hussein, into deep and multifaceted relations. This metamorphosis and paradigmatic change is a scientific issue and worthy of research. In this context, the main research question arises: what is the nature of the alliance in the relations of the Islamic Republic of Iran with Iraq in the post-Saddam era? The findings of the article indicate that the relations between the Islamic Republic of Iran and Iraq after Saddam have been based on a soft alliance. This alliance was created with the aim of countering a range of emerging threats and was not necessarily aimed at countering the hard and classical threats of a specific country. The soft alliance is institutionalized based on the multilateral commonalities of the two countries in various political, economic, and cultural fields, and at different sub-national and national layers between the two countries. The raw data in this article were collected using library methods and credible sources and processed analytically with a descriptive-analytical approach.