This article accounts for the formation of wh-questions and yes-no questions in English within the Minimalist Program of Chomsky (1993). Wh-words and such auxiliaries as do, have, be, and modal verbs in interrogative sentences are a -moved according to the economy principle of movement theory. In an interrogative construction wh-fronting and auxiliary movement arise from the necessity of fixing parameters and word order through morphological checking processes. To be checked off morphological properties of an interrogative sentence, lexical categories expressing meaning structure move to functional categories parameterizing syntactic structure. Constraints based on the economy principle, of course, are applied in the course of the morphological checking in a checking domain. With respect to morphological properties that should be checked off in wh-questions and yes-no questions, we propose that there exist three combinations of WH-feature and Q-feature in complementizer(=C) : [+ WH, +Q] for wh-extraction from an object or an adjunct, [+WH, -Q] for wh-extraction from a subject, and [-WH, +Q] for yes-no question formation. Other important condition for the formation of an interrogative sentence is that C has a tense operator which must be checked off by the tense operator feature of the tense verb in the tense domain C.

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