This dissertation introduces a methodology for formal specification and verification of user interfaces under security aspects. The methodology allows to use formal methods pervasively in the specification and verification of human-computer interaction. This work consists of three parts. In the first part, a formal methodology for the description of human-computer interaction is developed. In the second part, existing definitions of computer security are adapted for human-computer interaction and formalized. A generic formal model of human-computer interaction is developed. In the third part, the methodology is applied to the specification and verification of a secure email client.