The impact of the social networks-based sentiment analysis (SA) and opinion mining has increased in recent times. Decision-makers consider the opinions of the thought leaders and laymen, and plenty of opinions are available in social networks. When a user wants to get a service or buy a product he or she will check for the reviews and opinions provided by other people about various offerings. Opinion rich data sources are available in digital form; this attracts many researchers to focus research on SA. The 'sentiments' available in social networks and review pages are highly valuable for industries and individuals who want to closely monitor their reputation and live feedback about their services and products. This paper presents a review covering techniques, tools, data resources and applications in the area of textbased SA. Copyright © 2017 Inderscience Enterprises Ltd.