We investigate the complexity of counting Eulerian tours ({\sc #ET}) and its
variations from two perspectives---the complexity of exact counting and the
complexity w.r.t. approximation-preserving reductions (AP-reductions
\cite{MR2044886}). We prove that {\sc #ET} is #P-complete even for planar
4-regular graphs.
We introduce a new graph polynomial that encodes interesting properties of
graphs, for example, the number of matchings and the number of perfect
matchings. Most importantly, for bipartite graphs the polynomial encodes the
number of independent sets (#BIS).