Planar Laser Induced Fluorescence (PLIF) diagnostics based on the fluorescent intensity, lifetime, and/or quenching properties of organic molecules have been developed for a variety of applications: (1) Exciplex‐Based Vapor/Liquid Visualization systems provide spectrally‐separated emissions from the vapor and liquid phases and thus allow the separate visualization of the vapor and liquid phases of an evaporating fuel spray; (2) Exciplex Fluorescence Thermometry systems allow the measurement of liquid phase temperatures over the range 20–400 °C. Such systems have been used to measure the temperature of hydrocarbon droplets falling through heated nitrogen; (3) Streamlines by Oxygen Quenching, in combination with droplet‐slicing‐imaging, has allowed the visualization of internal circulation patterns within sub‐millimeter droplets hydrocarbon droplets; and (4) Fluorescence Lifetime Imaging, a technique which uses two PLIF images, one obtained a few nanoseconds after the other, has been applied to the imaging of the fuel/oxygen equivalence ratio in isothermal methane jets and to the imaging of temperature in oxygen‐free jets. This paper reviews the photophysical and diagnostic principles upon which the current systems are based and addresses their applications and limitations.