In this report, we will discuss algorithms to change speaker individuality: i.e., speech uttered by a speaker is changed or modified to sound as if another speaker had uttered it. First, we formulate voice conversion as a mapping problem by introducing vector quantization. Secondly, we propose a new algorithm which makes it possible to synthesize high quality speech even if the pitch frequency or duration is somewhat changed. Third, we discuss if speaker individuality can be controlled across different languages. Finally, to improve voice conversion performance, we propose also to convert the dynamic characteristics of speaker individuality by using speech segments as conversion units.