The Ialomiţa (Romanian: râul Ialomiţa) is a river of Southern Romania that rises from the Bucegi Mountains in the Carpathians and flows into the Danube.

The upper reach of the river is sometimes known as Valea Obârşiei or Obârşia Ialomiţei.

The largest cities along the Ialomiţa are Târgovişte and Slobozia.

The river Prahova is the major tributary to the river Ialomiţa.