Which Wikipedia policy addresses editors promoting their own interests?

The Wikipedia policy addressing editors promoting their own interests is Conflict of interest.

Wikipedia’s Conflict of interest guideline covers editing about oneself, family, friends, clients, employers, organizations, and other financial or personal relationships. It treats a conflict as a situation created by an external role or relationship—not automatically as proof of dishonesty, bad faith, or actual bias.

The guideline strongly discourages editors from directly changing affected articles. Instead, they can disclose the relationship and propose edits on the article’s talk page, where independent editors can review them. Paid contributors must disclose who is paying them, the client, and relevant affiliations under Wikimedia Foundation requirements.

A frequent mix-up is treating conflict of interest as a synonym for bias. Wikipedia distinguishes them: someone can be biased without having an external relationship to the subject, while a conflict can exist even when an editor believes they are acting neutrally. The guideline also does not ban every connected editor from participating; it emphasizes disclosure, restraint, independent review, and avoiding promotional or poorly sourced material.