The electric wave-filter, as regards its general transmission characteristics and its extremely important rôle in communication systems, is well known. Its physical theory was discussed in detail in the preceding number ot this Journal by its inventor, G. A. Campbell. In the present paper it is proposed to present systematic general methods of wave-til ter design, together with representative designs, which have been developed in connection with the practical utilization of this desile in the plant of the Bell System.