The local spin density approximation (LSDA) is used to investigate the interrelationships between electronic properties, magnetism, structure, and transport in La1−xCaxMnO3. The LSDA is shown to provide a realistic description of the endpoint compounds, including magnetic and structural symmetry. Mn–O hybridization is strong and spin dependent. Supercell calculations forx=1/4 andx=1/3 yield ferromagnetic configurations. Strong local La–Ca cation effects are found, which lead to localization of the low density of minority spin carriers in this regime. Implications of this effectively half‐metallic electronic structure are discussed.