© Springer International Publishing Switzerland 2017. This chapter presents the fundamentals of Faster-than-Nyquist (FTN) signaling. As originally introduced, FTN increases the bit-rate in the signaling bandwidth by packing symbols closer in time, at the cost of introducing intersymbol interference (ISI). We begin with the Euclidean distance properties of bandwidth efficient pulses at FTN rates and describe receivers that mitigate the severe ISI. The FTN achievable information rate is compared with the Nyquist information rate for practical pulses. We then discuss FTN extension to multicarrier systems with not only time packing but also subcarrier, optimizing both the time and frequency packing.