This paper focuses on the formal validation and verification of multi-modal human computer interfaces. It describes part of the obtained results of the French RNRT VERBATIM project whose purpose is the Multimodal Interfaces BIformal Verification and Test Automation. This project focuses on the application of a formal technique, namely the event B method. This approach is based on a proof technique and therefore it does not suffer from the state number explosion problem occurring in classical model checking. We outline the capability of this technique to support the design of multi-modal human computer interfaces, in particular, the capability to support the expression and the verification of properties issued from the CARE family. The proposed approach uses notations and semi-formal techniques issued from the HCI design area. We apply our approach on a case study called "CLIPS Yellow Pages".