  In this short paper we extend the classical Hoffman-Meeks Halfspace Theorem
to self-shrinkers, that is: "Let $P $ be a hyperplane passing through the
origin. The only properly immersed self-shrinker $\Sigma$ contained in one of
the closed half-space determined by $P$ is $\Sigma = P$."
  Our proof is geometric and uses a catenoid type hypersurface discovered by
Kleene-Moller. Also, using a similar geometric idea, we obtain that the only
complete self-shrinker properly immersed in an closed cylinder $ \overline{B
^{k+1} (R)} \times \mathbb{R}^{n-k}\subset \mathbb R^{n+1}$, for some $k\in
\{1, \ldots ,n\}$ and radius $R$, $R \leq \sqrt{2k}$, is the cylinder $\mathbb
S ^k (\sqrt{2k}) \times \mathbb{R}^{n-k}$. We also extend the above results for
$\lambda -$hypersurfaces.
