The present document defines the stage 3 specifications of the Supplementary Service Late Entry (SS-LE) for the Terrestrial Trunked Radio (TETRA). SS-LE allows radio users to be informed of and@ if they are concerned@ to join an already existing point-to-multipoint speech or data call. Man-Machine Interface (MMI) and charging principles are outside the scope of the present document. Supplementary Service stage 3 specification is preceded by the stage 1 and the stage 2 specifications of the service. Stage 1 describes the functional capabilities from the user's point of view. Stage 2 defines the functional behaviour in terms of functional entities and information flows. Stage 3 gives a precise description of the Supplementary Service from the implementation point of view. It defines the protocols for the service and the encoding rules for the information flows. It defines the processes for the functional entities and their behaviour. The described protocols and behaviour apply for the Switching and Management Infrastructure (SwMI) and for the Mobile Station (MS) and can be applied over the Inter-System Interface (ISI) between TETRA systems.