The structural and dielectric properties of (1−x)BaTiO3–xBiScO3 (x=0–0.5) ceramics were investigated to acquire a better understanding of the binary system, including determination of the symmetry of the phases, the associated dielectric properties, and the differences in the roles of Bi2O3 and BiScO3 substitutions in a BaTiO3 solid solution. The solubility limit for BiScO3 into the BaTiO3 perovskite structure was determined to be about x=0.4. A systematic structural change from the ferroelectric tetragonal phase to a pseudo-cubic one was observed at about x=0.05–0.075 at room temperature. Dielectric measurements revealed a gradual change from proper ferroelectric behavior in pure BaTiO3 to highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% BiScO3. Several of the compositions showed high relative permittivities with low-temperature coefficients of capacitance over a wide range of temperature. Quantification of the relaxation behavior was obtained through the Vogel–Fulcher model, which yielded an activation energy of 0.2–0.3 eV. The attempt characteristic frequency was 1013 Hz and the freezing temperature, Tf, ranged from −177° to −93°C as a function of composition. The high coercive fields, low remanent polarization, and high activation energies suggest that in the BiScO3–BaTiO3 solid solutions, the polarization in nanopolar regions is weakly coupled from region to region, limiting the ability to obtain long-range dipole ordering in these relaxors under field-cooled conditions.