This tutorial paper gives an overview of thei mplementation aspects related to turbo decoders, where the term turbo generally refers to iterative decoders intended for Parallel Concatenated Convolutional Codes as well as for Serial Concatenated Convolutional Codes. We start by considering the general structure of iterative decoders, and the main features of the SISO algorithm that forms the heart of iterative decoders. Then, we show that very efficient parallel architectures are available for all types of turbo decoders allowing high speed implementations. Other implementation aspects like quantization issues and stopping rules used in conjunction with buffering for increasing throughput are considered. Finally, we perform an evaluation of the complexities of the turbo decoders as a function of the main parameters of the code.