Hi, In the Boost Graph library, vertices have an index (vertex_index_t), and I was under the impression that edges have one, too. At least, there's a predefined type called edge_index_t. However, I can't figure out how to access an edge's index. For example, consider a graph defined like: typedef adjacency_list<vecS, vecS, directedS, Foo*> MyGraph; typedef graph_traits<MyGraph>::vertex_descriptor Vertex; typedef graph_traits<MyGraph>::edge_descriptor Edge; And let's say I've got a vertex descriptor called "u". I can iterate over u's outgoing edges like this: typedef graph_traits<MyGraph>::out_edge_iterator out_iter; std::pair<out_iter, out_iter> outp; for (outp = out_edges(u, g); outp.first != outp.second; ++outp.first) { Edge e = *outp.first; Vertex v = target(e, g); cout << index[v] << std::endl; // Works fine cout << index[e] << std::endl; // Compiler error } In this example, index[v] works as expected, but index[e] gives me a compiler error: "no match for ‘operator[]’ in ‘index[e]". Perhaps my graph typedef needs to be changed so that its edges have a property map for edge_index_t, although I'm not sure how to do that. (And anyway I wouldn't expect vertices to have indices by default but edges not...) Thanks for any help, Trevor