This book basically deals with the pseudo codes used in spread spectrum communication system. This includes the various types of pn codes and their techniques, benefits and shortcomings and as well as their properties. It has been seen that the length of the code, autocorrelation and cross correlation properties can be used to determine the best suitable code for any particular communication environment. Therefore, the code with suitable autocorrelation properties along with low cross correlation values was tried to find out. It was assumed only the bipolar case. At first, the best codes in 31 bit codewords which have the best auto-correlation properties were discovered. Then the work was concentrate on Walsh-Hadamard code. The Walsh-Hadamard code has the best cross correlation properties but it lacks self-synchronization feature. It was also tried to find out those codes in 64 Walsh-Hadamard codes which have best auto correlation properties. Finally the barker codes were analyzed. The barker code has good auto- correlation properties and the pair with the low cross correlation was discovered so that they can be used in multi-user CDMA environment.