Let $\mathcal{B}$ be an irreducible spherical Moufang building of rank at least $2$. Then the group $G$ is called a group of Lie type $\mathcal{B}$ if it is generated by the root subgroups corresponding to the roots of 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-known theorems of Seitz and Curtis and Tits, are obtained. 1991 Mathematics Subject Classification: 20G15, 20E42.