This paper is meant to present the Algerian experience of fighting the advances of desertification to northern Algeria by planting trees across the country.This green dam had been launched in the 1970s to prevent the overflow of the desert that threatened tens of millions of hectares.Its objective is planting of trees on 3 million hectares (1500 km long and average of 20 km wide) in the zone located between the 200 and 300 mm isohyets.The green dam concept was abandoned in the beginning of the 1990s and revived in 1995 as part of the agricultural and rural development schemes.The challenge is to ensure that the Sahara,which occupies 87％ of Algerian territory,does not advance further northward.Just for the last decade,some 70 000 ha were affected by desertification.Of the 238 million hectares of Algeria,200 million are occupied by the Sahara desert where socio-economic infrastructures are subject to siltation resulting from uncontrolled exploitation of natural resources of these sensitive environments.It is also mentioned that 32 million hectares forming the pre-Saharan steppe and are arid and semi-arid zones very sensitive to desertification process which is characterized by excessive grazing.Even in mountain areas with an area of 12 million hectares are not spared and are threatened by water erosion.A study of sensitivity to desertification conducted by the Algerian Space Agency (ASAL) has shown that over 45% of 27 million hectares,representing the size of the buffer zone between the desert and the north,composed of 12 province steppe,are seriously threatened by this natural phenomenon.