Electroluminescent devices based on polymeric materials have been a primary subject of research interest because of their potential for display and solid‐state lighting applications. These types of devices, termed polymer light‐emitting diodes, or PLEDs, offer the efficiency and lifetime benefits associated with solid‐state semiconductor technology, in addition to cost effective solution processing. Due to these inherent advantages, the field has grown rapidly over the past two decades, beyond the point of commercial exploitation. This article summarizes the exciting progress of the technology, addressing a broad range of topics including operating principles, device architecture, materials selection, and application requirements.