The volume LNCS 12287 constitutes the proceedings of the 27th International Workshop on Security Protocols, held in Cambridge, UK, in April 2019. The volume consists of 16 thoroughly revised invited papers presented together with the respective transcripts of discussions. The theme of this year's workshop was "Security Protocols for Humans" The topics covered included Designing for Humans and Understanding Humans, Human Limitations in Security, Secure sharing and collaboration and much more.