This volume LNCS 12927 constitutes the papers of the 18th International Conference on Trust, Privacy and Security in Digital Business, TrustBus 2021, held in September 2021 as part of the DEXA 2021 conference. The event was held virtually due to COVID-19 pandemic. The 11 full papers presented were carefully reviewed and selected from 30 submissions regarding advancements in the state of the art and practice of trust and privacy in digital business. The papers are organized in topical sections: Trust Evaluation; Security Risks; Web Security; Data Protection and Privacy Controls; and Privacy and Users