An echo question is a special type of interrogative which fully or partially reiterates a non-interrogative declarative uttered by a preceding conversation partner. It has the pragmatic effect of expressing surprise, requesting confirmation, or making an indirect negation. With respect to linguistic form, echo questions exhibit two cross-linguistic characteristics: First, as a type of putative interrogative, they do not use the typical syntactic devices of question formation. Second, they must take the sentence final rising intonation typical of interrogative sentences. It is argued in this article that the phonological characteristic can be derived from the joint effect of its syntactic characteristics and a cross-structural and cross-linguistic principle, while its syntactic characteristic itself can be analyzed as the shortened form of a tag question, where what is deleted in the shortened form are exactly those syntactic devices for question formation. The reason for the shortening is that the speaker utters the question too quickly due to the unexpectedness of the preceding declarative.