This document discusses duobinary signaling and modified duobinary signaling. Duobinary signaling is a form of partial response signaling where the pulse response spans two signaling intervals. Modified duobinary signaling corrects the deficiency of duobinary signaling having a nonzero frequency response at the origin by using a class IV partial response. It achieves a spectral shape with a gradual cutoff but requires a larger SNR to achieve the same error probability compared to binary signaling.