Distributed generation systems are going to play a vital role in modern power systems. These types of systems are directly linked with the consumer load terminals. Introduction of these types of systems into existing system will provide innumerable advantages. However, the design parameters like sizing and optimal location is a challenging task. The objective of ODG (OPTIMAL DG) is to influence the efficiency of the system with minimum power loss, high system security, reliability and voltage stability. A different type of techniques has come into existence varying from simple systems to most complicated systems. Analytical techniques are best suitable for simple systems. Meta-heuristic technology can be used for complex systems for achieving high accuracy. A hybrid optimization technique uses two or more ways for achieving the better results. In this paper, a detailed review of DG basics and different methods of DG integration into the existing system are studied. In further, all the four types of methods are compared with pros and cons. This paper will give insight of the ODG allocation and sizing in a distribution system.