  In the present paper we define conservative and semiconservative random walks
in $\mathbb{Z}^d$ and study different families of random walks. The family of
symmetric random walks is one of the families of conservative random walks, and
simple (P\'olya) random walks are their representatives. The classification of
random walks given in the present paper enables us to provide a new approach to
random walks in $\mathbb{Z}^d$ by reduction to birth-and-death processes. We
construct nontrivial examples of recurrent random walks in $\mathbb{Z}^d$ for
any $d\geq3$ and transient random walks in $\mathbb{Z}^2$.
