This is a short rewiew of some taxonomic, morphologic and ecophysiological aspects of lichens in arid regions, incorporating some of our own data. Percentages of dominant genera and life forms are, in Spanish arid regions (Ebro Valley, Almería and Murcia), close to the figures given for classical extraeuropean deserts and semideserts. Relationship with Californian arid regions is commented. Ecophysiological adaptations include improved absorption of atmospheric water. Dew and high relative air moisture conditions in Los Monegros (Ebro Valley) are summarized. The main morphological adaptations are: thick and/or pigmented cortical layer, pruina, exposure to early morning light of algal layer after night water intake, grouping of algae in vertical glomerulli, etc.