A composite wafer includes in this order: a support substrate; an amorphous layer; and a SiO2-containing substrate. The amorphous layer is in contact with a first adjacent layer and a second adjacent layer, and includes an element included in each of the first adjacent layer and the second adjacent layer. A composite wafer of another embodiment of the present disclosure includes in this order: a support substrate; an amorphous layer; and a SiO2-containing substrate having a OH group content of 100 ppm or less. The amorphous layer is in contact with a first adjacent layer and a second adjacent layer, and includes an element included in each of the first adjacent layer and the second adjacent layer. A method of producing a composite wafer of an embodiment of the present disclosure includes directly joining a support substrate and a SiO2-containing bulk.