Let $\mathcal{B}$ be an irreducible spherical Moufang building of rank at least $2$. Thenthe group $G$ is called a group of Lie type$\mathcal{B}$ if it is generated by theroot subgroups corresponding to the rootsof some apartments of $\mathcal{B}$. This notion includes:\begin{enumerate}\item[(1)] classical groups of finite rank,\item[(2)] simple algebraic groups over arbitrary fields,\item[(3)] the `mixed' groups of Tits.\end{enumerate} General structure theorems and a general presentation type theorem for such Lie-type groups, which in a way generalize well-knowntheorems of Seitz and Curtis and Tits, are obtained. 1991 Mathematics Subject Classification:20G15, 20E42.