Increasing the spectral efficiency and per channel data rate have historically been shown to be the most cost-effective method to meet the need of ever growing capacity demand in the core network. In this paper we review recent progress in high-speed and high-spectral-efficient optical transmission technology. We discuss spectrally efficient modulation and detection technologies that have been experimentally explored for future 100-Gb/s and above optical transmission system. Emerging methods aiming at extending system reach for noise and nonlinearity-stressed high spectral efficiency optical transmission systems have also been reviewed. We show that spectrallyefficient multilevel coding coupled with polarization multiplexing and digital coherent detection has the potential to enable 400Gb/s per channel WDM system operating with existing 50GHzspaced WDM infrastructure at a spectral efficiency of 8b/s/Hz. Increasing the spectral efficiency and per channel data rate have historically been shown to be the most cost-effective method to meet the need of ever growing capacity demand in the core network. In this paper we review recent progress in high-speed and high-spectral -efficient optical transmission technology. We discuss spectrally efficient modulation and detection technologies that have been experimentally explored for future 100-Gb / s and above optical transmission system. Emerging methods aiming at extending system reach for noise and nonlinearity-stressed high spectral efficiency optical transmission systems have also been reviewed. We show that spectrallyefficient multilevel coding coupled with polarization multiplexing and digital coherent detection has the potential to enable 400Gb / s per channel WDM system operating with existing 50GHzspaced WDM infrastructure at a spectral efficiency of 8b / s / Hz.