Globally hyperbolic spacetimes with timelike boundary $(overline{M} = M cup partial M, g)$ are the natural class of spacetimes where regular boundary conditions (eventually asymptotic, if $overline{M}$ is obtained by means of a conformal embedding) can be posed. $partial M$ represents the naked singularities and can be identified with a part of the intrinsic causal boundary. Apart from general properties of $partial M$, the splitting of any globally hyperbolic $(overline{M},g)$ as an orthogonal product ${mathbb R}times bar{Sigma}$ with Cauchy slices with boundary ${t}times bar{Sigma}$ is proved. This is obtained by constructing a Cauchy temporal function $tau$ with gradient $ abla tau$ tangent to $partial M$ on the boundary. To construct such a $tau$, results on stability of both, global hyperbolicity and Cauchy temporal functions are obtained. Apart from having their own interest, these results allow us to circumvent technical difficulties introduced by $partial M$. As a consequence, the interior $M$ both, splits orthogonally and can be embedded isometrically in ${mathbb L}^N$, extending so properties of globally spacetimes without boundary to a class of causally continuous ones.
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