Sinkhole attack is an active attack, launched in a Wireless Sensor Network by compromising a legitimate node or by introducing a malicious node in order to gain the traffic routed towards it before reaching the base station, by making a false advertisement in the routing information of its nearest distance to reach the base station. Due to this fake information the data packets under transmission are routed towards the malicious node through which the attacker can gain the access to the information, tamper the information or may even destroy it. Thus, this attack causes a severe threat to the normal functionality of the Wireless Sensor Network. Because of the wider range of applicability of Wireless Sensor Networks in our day-to-day life and in future the detection and mitigation of Sinkhole attack plays a vital role. In this view, a survey on the existing mechanisms to detect and mitigate the Sinkhole attack, their advantages and drawbacks is being documented by us in this paper.