This book basically gives the over view about The properties of erbium-doped fiber amplifier (EDFA) such as gain and noise figure have been studied. By determining the characteristics of the 980nm, 1480nm & 1550nm laser sources and ASE (amplified spontaneous emission) at the output of the amplifier used to determine the gain and noise figure of EDFA. This model allows to follow the signal (1550nm), pump (980nm) and ASE as they propagate along the fiber and determine population inversion .The both forward and backward propagation ASE are important in determining the overall gain and noise figure. For the amplification of more than 80 channels the DWDM (Dense Wavelength Division Multiplexing) has required C-Band (1525-1565)nm and L-Band (1565-1610)nm EDFA.We show that a flat gain spectrum can be achieved in the range from 1565 to 1610 nm when the EDF length, pump power and pump configuration are appropriately chosen. Special care must be taken when selecting the EDF length.