The present study examines the effect of transfer pricing, book–tax differences, and underinvestment on tax avoidance practices in the Tehran Stock Exchange. Methodologically, the study is descriptive in nature and applied in purpose. Since the current status of the variables was analyzed through the collection of historical data, the research is classified as descriptive and ex post facto. The variables are quantitative, and the data were gathered from the website of the Securities and Exchange Organization. Three hypotheses were formulated, and 144 firms were selected through systematic elimination sampling for a six‑year period from 2019 to 2024. After data collection in Excel, the variables were analyzed using EViews and Stata statistical software. The results of hypothesis testing indicate that transfer pricing has a direct effect on tax avoidance practices, book–tax differences have a direct effect on tax avoidance practices, and underinvestment also has a direct effect on tax avoidance practices.