The current emphasis in second language teaching lies in the achievement of communicative effectiveness. In line with this approach, pronunciation training is nowadays geared towards helping learners avoid serious pronunciation errors, rather than eradicating the finest traces of foreign accent. However, to devise optimal pronunciation training programmes, systematic information on these pronunciation problems is needed, especially in the case of the development of Computer Assisted Pronunciation Training systems. The research reported on in this paper is aimed at obtaining systematic information on segmental pronunciation errors made by learners of Dutch with different mother tongues. In particular, we aimed at identifying errors that are frequent, perceptually salient, persistent, and potentially hampering to communication. To achieve this goal we conducted analyses on different corpora of speech produced by L2 learners under different conditions. This resulted in a robust inventory of pronunciation errors that can be used for designing efficient pronunciation training programs. (Contains 2 figures, 14 tables and 15 notes.)