Merdare border crossing

The Merdare border crossing joins the de facto independent republic of Kosovo (near Prishtina) with Serbia (near Niš). It lies on the E80. Walking across this border is allowed.

Into Kosovo

You can thumb just after passport control, before the small roadside cafe. If you are going to Prishtina, wait for a direct lift instead of being dropped off somewhere before Prishtina.

Into Serbia

Crossing from Kosovo into Serbia is generally a longer process. Most importantly, if you've entered Kosovo directly (i.e. from Albania, Macedonia, Montenegro, or by flying) without first entering Serbia you are quite likely to be denied entry to Serbia for having "illegally entered Serbia" (officially Serbia still considers Kosovo to be Serbian territory). The border guards will know because you do not have a Serbian visa stamp in your passport. In this case, the Serbian officers will insist you enter through Montenegro or Macedonia instead.