[en] Manganites of the series (La_1-xCa_x)MnO₃, with x = 0, 0.1, 0.3, 0.5, 0.7 and 1.0, have been characterized in ceramic form and thin films have been prepared by pulsed laser deposition. Characterization techniques included x-ray diffraction, conductivity and magnetoresistance, magnetization and susceptibility, optical spectroscopy and the Faraday effect. Both the films and ceramics exhibit a maximum low-temperature conductivity at x approx. 0.3 which is coexistent with ferromagnetic order. The negative magnetoresistance effect is qualitatively different for the x=0.3 and x=0.5 compositions. For x=0.3 the magnetoresistance peak occurs around the Curie point, whereas for x=0.5 the onset of magnetoresistance is somewhat below T_c and increases monotonically as T→0. The applied field appears to modify the magnetic order (on the scale of the spin diffusion length) down to the lowest temperatures for x=0.5, but for x=0.3 the ferromagnetic order is essentially complete and collinear below the Curie point. (author)