This work is devoted to the study on Polymer Light- Emitting Diodes (PLEDs) based on polyfluorenes, a promising class of semiconductive polymers for light-emitting diode applications. It covers theories of PLEDs, literature overview of polyfluorene-based light-emitting diodes, as well as research results by the authors. In this study, several types of PLED devices based on neat polyfluorenes or polyfluorene blends were designed, fabricated, and characterized. The electrical characteristics of two neat polyfluorenes were simulated via using space charge limited current theory for the hole-only case and/or exploiting a commercial software package.