LEACH is a hierarchical protocol in which most nodes transmit to cluster heads, and the cluster heads aggregate and compress the data and forward it to the base station (sink).In LEACH, a TDMA-based MAC protocol is integrated with clustering and a simple “routing” protocol. The goal of LEACH is to lower the energy consumption required to create and maintain clusters or to use the energy of the nodes in such a manner so as to improve the life time of a wireless sensor network. In this paper we are presenting an overview of the different protocol changes made in LEACH to improve network lifetime, throughput, coverage area of network etc. Keywords-LEACH, E-LEACH, Enhanced LEACH, EHE-LEACH, Multi-level Leach 1. LEACH: PROTOCOL EXPANATION LEACH, Low-energy Adaptive Clustering Hierarchy, presented by Wendi B. Heinzelman of MIT, is application specific protocol architecture for Wireless Sensor Network (WSN). It assumes a dense sensor network of homogeneous, energy-constrained nodes, which shall report their data to a sink node. It has become one of the most used bases for developing new architecture protocols or modifying the existing one in WSN. LEACH [6] is a TDMA-based MAC protocol which is integrated with clustering and a simple routing protocol in wireless sensor network. LEACH partitions the nodes into clusters and in each cluster a dedicated node, the clusterhead, is responsible for creating and maintaining a TDMA schedule; all the other nodes of a cluster are member nodes. To all member nodes, TDMA slots are assigned, which can be used to exchange data between the member and the clusterhead; there is no peer-to-peer communication. Except their time slots, the members can spend their time in sleep state. The clusterhead aggregates the data and transmits it to the sink. Since the sink is often far away, the clusterhead must spend significant energy for this transmission. For a member, it is typically much cheaper to reach the clusterhead than to transmit directly to the sink. The clusterheads role is energy consuming since it is always switched on and is responsible for the long-range transmissions. If a fixed node has this role, it would burn its energy quickly, and after it died, all its members would be “headless” and therefore useless. Therefore, this burden is rotated among the nodes. Specifically, each node decides independent of other nodes whether it becomes a clusterhead, and therefore there is no signalling traffic related to clusterhead election (although signalling traffic is needed for subsequent association of nodes to some clusterhead). This decision takes into account when the node served as clusterhead the last time, such that a node that has not been a clusterhead for a long time is more likely to elect itself than a node serving just recently. The protocol is round based, that is, all nodes make their decisions whether to become a clusterhead at the same time and the nonclusterhead nodes have to associate to a clusterhead subsequently. The nonclusterheads choose their clusterhead based on received signal strengths. The network partitioning into clusters is time variable and the protocol assume global time synchronization. After the clusters have been formed, each clusterhead picks a random CDMA code for its cluster, which it broadcasts and which its member nodes have to use subsequently. This avoids a situation where a border node belonging to clusterhead A distorts transmissions directed to clusterhead B, shown in Figure1.