Factors affecting the performance of filamentary scintillators are considered. Experimental data on light attenuation for both plastic scintillator filaments and thin‐wall glass tubing liquid scintillators are presented. A theoretical interpretation which satisfactorily accounts for the performance of luminescent filaments in terms of bulk properties and surface reflection losses is given and permits quantitative evaluation of surface losses for various materials. While plastic scintillator fibers are mechanically convenient, it is suggested that liquid‐filled fibers will prove more consistent and stable in their properties. Comments on the utility of arrays of fibers as particle track imaging devices and as image intensifier screens are included.