This article discusses Eulerian circuits and trails in graphs. An Eulerian circuit is a closed trail that contains every edge of a graph, and an Eulerian trail is an open trail that contains all the edges of a graph but doesn't end in the same start vertex. This article also explains the Königsberg Bridge Problem and why it's impossible to find a trail in it. Finally, there are two implementations in C++ to find Eulerian trails in directed and undirected graphs.