Sentiment analysis is also known as opinion mining which it extracts opinions to learn about public point of view. In general, people prefer to take advice from others not only to get sensible products but also to invest in a wise way. Nowadays, the popular sources of personal opinion are blogs. The consumer review sites are helpful to know about the features and services available to a specific product. This sentiment analysis is also helpful to the manufactures to improve their business by knowing the public opinion. The online sources gather public opinion content in the form of blogs, forums, social media, review websites, etc. The sentiment analysis automatically mines the huge content that is available online. This paper gives a complete study of various supervised and unsupervised classifiers.