This chapter is an attempt to survey the predictions of some of the most important factors involved in attrition and to discuss them with respect to empirical data from L1 attrition. The factors discussed include biological aspects (plasticity, activation thresholds, inhibition and emotional implication), cognitive aspects (memory, aptitude, literacy and task dependency) and external factors (the role of language use, the cultural context and attitudes). The discussion shows that (a) many of these factors are closely linked, (b) some of them may be considered cluster factors which are more influent and more strongly interrelated than others, and (c) none of the factors may alone be considered responsible for attrition. This may be accounted for by a multicomponential view of language attrition.