This chapter shows that for any process in a network that initially only knows its neighbors, it is possible to get to know the entire network graph by network-wide message passing. For this purpose, the concept of heartbeat algorithms is developed. A simple solution to this problem works with a representation of graphs in the form of adjacency matrices. This assumes that each process has as the number of processes in it (to determine the size of this matrix) and the diameter of the network graph as global information about the network. This limitation leads to the development of a graph-based algorithm that is able to do this without this global knowledge.