We defined the cellular mechanisms for genesis, migration, and differentiation of the initial population of olfactory bulb (OB) interneurons. This cohort of early generated cells, many of which become postmitotic on embryonic day (E) 14.5, differentiates into a wide range of mature OB interneurons by postnatal day (P) 21, and a substantial number remains in the OB at P60. Their precursors autonomously acquire a distinct identity defined by their position in the lateral ganglionic eminence (LGE). The progeny migrate selectively to the OB rudiment in a pathway that presages the rostral migratory stream. After arriving in the OB rudiment, these early generated cells acquire cellular and molecular hallmarks of OB interneurons. Other precursors--including those from the medial ganglionic eminence (MGE) and OB--fail to generate neuroblasts with similar migratory capacity when transplanted to the LGE. The positional identity and migratory specificity of the LGE precursors is rigidly established between E12.5 and E14.5. Thus, the pioneering population of OB interneurons is generated from spatially and temporally determined LGE precursors whose progeny uniquely recognize a distinct migratory trajectory.