The universal use of herbicides in agriculture creates a necessary to study the effect of these chemicals on non-target organisms such as algae, which are sensitive to herbicides where they share with higher plants many common characters. So this book aimed at studying the effect of two herbicides glyphosate and clodinafop-propargyl which are currently used in Egypt on soil algae, as well as, to study the effect of these herbicides on the growth and some metabolic activities of some algae such as Scenedesmus quadricauda (Chlorophyta) and Merismopedia glauca (Cyanophyta) which isolated from the soil.