The present document provides usability guidelines relating to the development and implementation of UCI systems. EG 201 940 [1] and EG 202 067 [2] identified the critical importance of the usability issues associated with Universal Communications Identifier (UCI) systems. TR 103 077 [3] has identified usability best practice relating to advanced communication services. It has discussed the implications of applying such best practice to the user tasks necessary for implementation of UCI based services whilst still meeting the relevant User Requirements defined in EG 201 940 [1]. TR 103 077 [3] also defined areas relating to usability which would be suitable for the production of guidelines. The guidelines are numbered consecutively throughout each clause in order to relate them to the context in which they apply. The present document also highlights areas in which it is not currently possible to define guidelines. Such instances will be because: ? there is insufficient research or experience relating to a particular usability issue; ? certain technical aspects of UCI system are insufficiently evolved or defined; ? there is a need for focussed consultation with specialized groups of users such as elderly people@ people with disabilities@ young children and people from non-European cultures; ? simple guidelines may not be able to adequately address the usability issues associated with a complex functionality. Where guidelines have not been provided@ it has sometimes been possible to highlight usability issues that should focus designers' attention on specific areas that are critical to system usability. In dealing with the usability issues@ it would be expected that designers should make use of usability design techniques such as: ? focus groups for formalized user requirements capture; ? task analysis; ? user trials. Use of these techniques is advisable even where the guidelines in the present document are being used. Ideally@ the present document@ which defines usability guidelines@ should be read in conjunction with TR 103 077 [3] which describes the background to all Guidelines. To avoid the need for constant cross-referencing between the two documents@ much relevant text from TR 103 077 [3] has been duplicated in the present document. The present document will provide information and guidance for: ? terminal and service designers (telecommunications and IT); ? service providers (telecommunication and IT); ? designers of external tools (e.g. calendar@ address book) that may be used in a UCI context; ? user groups; ? other Technical Committees within ETSI.