  An introduction to inhomogeneous Poisson groups is given. Poisson
inhomogeneous $O(p,q)$ are shown to be coboundary, the generalized classical
Yang-Baxter equation having only one-dimensional right hand side. Normal forms
of the classical $r$-matrices for the Poincar\'{e} group (inhomogeneous
$O(1,3)$) are calculated.
