  Let $X(\cdot) $ be a random field $\mathbb{R}^D \to \mathbb{R}^d$, $D\geq d$.
We first studied the level set $X^{-1}( u) $, $u \in \mathbb{R}^d$. In
particular we gave a weak condition for this level set to be rectifiable. Then,
we established a Kac-Rice formula to compute the $D-d$ Hausdorff measure. Our
results extend known results, particularly in the non-Gaussian case where we
obtained a very general result. We conclude with several extensions and
examples of application, including functions of Gaussian random field, zeroes
of the likelihood, gravitational microlensing, shot-noise.
