What are the competences which establish interpreters as professionals? In relation to this question, this paper examines professional interpreters` memory system. Research on interpreters` memory in recent years has revolved around the working memory in simultaneous interpreting. Results of those researches were however highly contradictory. To find out the reasons for those disappointing results and to understand better, in which form each kind of memory serves to the complex task of interpreting, a more comprehensive treatment of the theme “memory” appears required. First, this paper reviews various memory types as commonly defined in cognitive psychology. The paper`s hypothesis is constructed upon how each memory type is employed in both consecutive and simultaneous interpreting. Finally, hypothetical conclusions are drawn: (1) As for long-term memory, not its capacity but its structure might differ from non-interpreters, and (2) short-term memory plays a key role in consecutive interpreting. Stimuli which retrieve interpreters` STM are either previous informations or note-taking which work as a firework in retrieving series of memory chains in interpreters` brain. (3) To verify the hypothesis that professional interpreters have a greater working memory capacity than non-professionals one should measure their semantic memory, and not their auditive or visual memory.