Speaker Diarization is the task of identifying start and end time of a speaker in an audio file, together with the identity of the speaker i.e. “who spoke when”. Diarization has many applications in speaker indexing, retrieval, speech recognition with speaker identification, diarizing meeting and lectures. In this paper, we have reviewed state-of-art approaches involving telephony, TV shows, broadcasting and meeting data. Along with the state-of-art approaches, the major approaches that are commonly used in diarization are reviewed. Few possible future directions of this technology are also identified.