This guide provides new data on the biodiversity of Algeria through the flora and vegetation of the steppes and Sahara. By proposing a phytosociological typology, it constitutes the link in a chain that will make it possible to elaborate a system of Algerian vegetation. Because of the diversity of its ecosystems, the Sahara cannot be associated with a "desert": "plant life" is present in ecological habitats (reg, hamada, erg, oued, sebkhas, adrars) where the frequency of arborescent or shrubby taxa is remarkable: nearly 50% of the trees and shrubs of Algeria are listed. In the Sahara, trees are of inestimable value: tarout, b'tom, argan and many other species are witnesses to the paleo-climatic vicissitudes that have affected the Sahara since the Tertiary era. The population is highly dependent on the flora and vegetation, which continue to provide a wide range of ecosystem services essential to their needs in terms of food, care, shelter, fuel, fodder for the many flocks of sheep and goats, etc.