  Consider a sub-Riemannian geometry $(U,D,g)$ where $U$ is a neighborhood at 0
in $\R^n,$ $D$ is a rank-2 smooth $(C^\infty $ or $C^\omega)$ distribution and
$g$ is a smooth metric on $D$. The objective of this article is to explain the
role of abnormal minimizers in SR-geometry. It is based on the analysis of the
Martinet SR-geometry.
