An ideal optical regenerator transforms the degraded bitstream into its original form by performing three functions: reamplification, reshaping, and retiming. Optical signals propagating in fiber-optic transmission systems are affected by several effects, namely amplified spontaneous emission (ASE) from optical amplifiers, chromatic dispersion, polarization-mode dispersion, and nonlinear phenomena. Considering the impairments imposed by these effects. In this chapter we review the need, general principles and approaches used to regenerate mainly phase encoded signals of differing levels of coding complexity. The documents may come from teaching and research institutions in France or abroad, or from public or pri-vate research centers. 1R Regeneration: Analog amplification Can provide gain but also adds noise. One example is the Schmitt trigger.