This paper examines the role of different factors in the microstructure of ceramic YBa2Cu3O7-delta with emphasis on its electrical response. In particular we discuss: 1. the effect of microstructural variations on j(c) and rho(300), 2. measurement of j(c), 3. the presence of minor phases and carbonates, 4. oxygen uptake and microcracks, 5. plastic deformation and related structural defects.