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.