  In this partly expository paper we discuss and describe some of our old and
recent results on partial orders on the set (m,n)-graphs (i.e. graphs with n
vertices and m edges) and some operations on graphs that are monotone with
respect to these partial orders. The partial orders under consideration include
those related with some Laplacian characteristics of graphs as well as with
some probabilistic characteristics of graphs with randomly deleted edges.
Section 2 provides some notions, notation, and simple observations. Section 3
contains some basic facts on the Laplacian polynomial of a graph. Section 4
describes various graph operation and their properties. In Section 5 we
introduce some partial orders on the set of (m,n)-graphs related, in
particular, with the graph Laplacian and the graph reliability (Laplacian
posets and reliability posets}). Section 6 contains some old and recent results
on the monotonicity of some graph operations with respect to Laplacian posets.
Section 7 and 8 include some old and recent results on the monotonicity of some
graph operations with respect to reliability posets and to some other
parameters of graphs as well as some open problems. Section 9 contains some
generalizations of the described results on weighted graphs.
  Keywords: graph, graph operations, graph posets, random graphs, decomposable
graphs, threshold graphs, weighted graphs, spanning subgraphs, Laplacian
polynomial and spectrum, adjacency polynomial and spectrum, graph reliability,
trees, forests, Hamiltonian cycle and path, symmetric polynomials
