This thesis presents the results of a series of experiments aimed at evaluating the effect of L2 experience on the perception and production of both L1 and L2 stops. Eight L1-English/Spanish L2-Spanish/English mirror-image groups varying in amount of L2 experience participated in the study. Perception was examined by using an identification task involving a voice onset time continuum. Production was collected by means of sentence reading tasks. Perception results showed a positive effect of L2 experience on L2 perception and a detrimental effect on L1 perception in the case of the L1-Spanish speakers, whereas no effect was observed regarding the English groups. All groups seemed to perform similarly in the L1 and in the L2. As for production, no effect of L2 experience was revealed on L1 production for any group, whereas a positive effect of experience was found on L2 voiceless stop production – i.e., the greater the amount of L2 experience, the more target-like the learners’ productions were. L2 voiced stops posed a greater challenge than L2 voiceless stops. In general, learners produced significant differences between L1 and L2 stops, particularly the English learners of Spanish. Overall, it appears that L2 experience has a greater effect on the L2 than on the L1. Moreover, a more straightforward influence of L2 experience was observed in production than in perception, especially regarding voiceless stops. These results are discussed in terms of their contribution to L2 speech models on cross-linguistic influence.