This thesis deals with the merge operation in the four types of languages in the world, namely internal merge of displaced wh-words or wh-phrases in Single Filled Spec Languages, Multiply Filled Spec Languages, and Non-multiply Filled Spec Languages, and external merge of in situ wh-words and wh-phrases in Null Spec Languages. The universality of merge in the wh-questions proves that merge is a biologically based operation.