The future establishment of large telescopes at the Observatorio del Roque de los Muchachos (ORM) has raised the necessity of designing a site-testing campaign, aimed specifically at selecting their emplacements, as well as characterizing correctly the local seeing behavior and the fluctuations of the turbulent field in the area covered by the observatory. This paper describes the site evaluation program to be carried out at the ORM during the next four years. The data obtained in this program will improve earlier tests in the critical areas of sub-arc sec seeing, the size of the isoplanatic patch, the 'efecto Caldera,' and suitability for infrared astronomy, among others.