This paper summarizes the design and development of a 4-frequency selective surface (FSS) for the NASA Cassini high gain antenna (HGA). Specifically, two FSS/HGA design approaches were considered for multiplexing the four frequency bands (S-, X-, Ku-, and Ka-band) of the Cassini Project. In the first approach (with two transmit and two reflect bands), a double screen FSS with double ring patch elements was developed to transmit the S- and Ku-band signals and to reflect the X- and Ka-band signals. However, this FSS presents relatively high insertion loss at the S-band. Therefore, the second approach (with one transmit and three reflect bands) was developed, using a single screen FSS with double square loop slot elements to transmit the Ka-band and to reflect the S-, X-, and Ku-band waves. Significant improvement in the S-band loss performance is obtained with this second approach. However, it will require a dual reflector shaping study to optimize the subreflector size for minimizing the spill over and blockage losses.