This research aims to examine the impact of the external auditor's industry specialization on investor decisions. The study was applied to three private commercial banks listed on the Iraqi Stock Exchange during the period from 2020 to 2022. The variables were quantitatively measured based on the annual financial reports of a sample of Iraqi banks listed on the Iraqi Stock Exchange. The weighted market share measure was used, which is calculated by multiplying the market share ratio by the portfolio share ratio to assess the level of industry specialization of the auditing companies that audited the selected banks in the sample. As for investors' decisions, they were measured based on the trading value of the stocks of each company during the year, as investor economic decisions are reflected in their buying, selling, or holding of stocks, which in turn impacts the traded stock value, one of the key findings of the study is that the external auditor's industry specialization plays an important role in supporting investors' decisions. Industry specialization helps maintain trust in the credibility and integrity of financial reports, thanks to the auditor's knowledge and professional competence, which enhances the auditor's ability to detect illegal activities in financial statements. This creates a level of trust among stakeholders, positively impacting their investment decisions and ensuring that their investments are made in a sound manner. The statistical analysis results showed that there is a significant effect of the external auditor's industry specialization on investors' decisions.