Chlorophyll (also chlorophyl) is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros ("green") and φύλλον, phyllon ("leaf"). Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to absorb energy from light. Chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. However, it is a poor absorber of green and near-green portions of the spectrum, hence the green color of chlorophyll-containing tissues. Chlorophyll was first isolated by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817.

Chlorophyll gives leaves their green color and absorbs light that is used in photosynthesis.

Chlorophyll is found in high concentrations in chloroplasts of plant cells.

Absorption maxima of chlorophylls against the spectrum of white light.^{[citation needed]}.

SeaWiFS-derived average sea surface chlorophyll for the period 1998 to 2006.