Input and output devices are connected to CPU by a number of cables or lines. These lines are called buses in computer terminology. Bus is a communication system that transfers data between components in a computer system. There are basically 3 types of buses namely; address bus, data bus and control bus. The address bus carries the address of memory or I/O device that is required by CPU. This bus is also called A bus. The data bus is used to transfer data between processors, memory and I/O devices. The data bus is bi-directional bus having the width equal to the word length. This bus is also called D bus. The control bus carries control signals. There are mainly three types of bus organizations namely single bus organization, two bus organization and multiple bus organization. This document explains the different type of buses, different organizations and its merits and demerits in detail.