Adult neurogenesis in the dentate gyrus of the hippocampus has gained considerable attention as a cellular substrate for both the pathophysiology and treatment of depression. Overall, the studies of adult hippocampal neurogenesis are still in their infancy because most of them explore only one stage of this process. Importantly, given the built-in homeostatic mechanisms that act at each stage during the progression from stem cells to mature neurons (proliferation, differentiation, maturation, survival), it is very difficult to extrapolate the efficiency of a drug on adult neurogenesis from analysis of one stage alone. Here, we review the most significant data on hippocampal neurogenesis, focusing on the importance of studying each stage of adult hippocampal neurogenesis and also on the importance of choosing the appropriate mouse strain to perform the experiment. Specifically, strains with a high number of basal proliferating cells in the dentate gyrus of the hippocampus should be used only under stressed conditions to detect the effects of antidepressants on adult neurogenesis. We also discuss how adult hippocampal neurogenesis could be involved in affective state disorders such as depression and anxiety. Finally, we reveal that the behavioral effects of fluoxetine are mediated through both neurogenesis-dependent and -independent actions.