Astrocytes display extensive molecular, morphological, and functional diversity, but how this diversity emerges during development remains unclear. In this thesis, single-cell and spatial transcriptomics were combined with DNA barcoding to define neocortical astrocyte subtypes and trace their lineage origins. Five molecular astrocyte subtypes were identified in the mouse neocortex, each showing distinct spatial distributions across cortical layers and white matter. Developmental trajectory analyses revealed that these subtypes arise from two major differentiation programs. TrackerSeq lineage tracing further showed that one astrocyte-producing lineage derives from Emx1-positive radial glial cells that first generate excitatory neurons, whereas a second lineage produces few neurons and preferentially gives rise to Olig2-marked astrocytes. Olig2 knockout disrupted lineage allocation, altered astrocyte molecular identity and morphology, and impaired pro-synaptogenic functions. Together, these findings show that neocortical astrocyte diversity is partly prefigured by intrinsic lineage programs and contributes to circuit maturation.