This study examined cross-directional development on the production and perception of L2 prosody features. The results of the experiments suggest that (1) L2 developmental patterns of production and perception clearly have been influenced by L1 system, and (2) both production and perception in L2 might develop together over the length of the immersion experience after the critical period. It is essential for teachers to understand why L2 learners produce various L2 speech depending on L1 and immersion experience. I suggest that L2 speech variations result from asymmetry relations between production and perception and that these could be removed by the qualified immersion experience even for adult L2 learners. This book is intended as a reference for bilingual researchers and educators.