Pressure effects in the iodine-containing p pi-d system (DCNQI)(2)Cu are mainly described. Electrical and magnetic properties of (R(1),R(?)2-DCNQI)(2)Cu are quite sensitive to the substituents R(1) and R(2). A variety of substituent effects would be generally understood in terms of the amount of charge transfer from Cu to DCNQI which is sensitive to the N-Cu-N coordination angle. In the iodine-containing DCNQI-Cu system, however, an inter-stack LUMO ... LUMO interaction would also play an important role.