Abstract : Relations involving the frequency-dependent optical constants give information on the electronic properties of solids. Power reflectivity measurements at normal incidence over a wide frequency region can be utilized in obtaining the optical constants by means of a general integral transformation known as the Kramers-Kronig transformation. A computer program based on this integral transformation has been constructed in Fortran II, version 9000, language for a Remington Rand Solid State 90 computer. The program converts experimental reflectivity measurements into parameters containing the optical constants. A brief presentation of the electronic quasiparticle and collective excitation modes is given in terms of the optical constants. A discussion of the approximations made in putting the integrals on the computer is also given. Two tests were made to check the accuracy of the program. First, a test reflectivity function, for which the Kramers-Kronig integrals could be directly evaluated, was programmed. Then published reflectivity measurements on copper were analyzed. The optical constants determined by the computer program were in good agreement with both the test optical constants and the previously calculated constants of copper.