This book explains briefly the fundamentals of digital communication techniques. So that, it shows firstly the advantages of using digital communication systems and it demonstrates how can convert the analog signals to digital signals. In addition to that, it states the types and features of using digital and pulse modulation types as well as the multiplexing techniques. Also the reasons of creating InterSymbol Interference (ISI) and the reduction methods are discussed. Finally, it explains the operation of Matched filters and how it can detect the digital signals in noisy channels.