A quarter century of innovation in the development of packaging for semiconductors has culminated in the announcement of the IBM 4300 Series of computers and the IBM 3081. This technology has been built on a broad and expanding base starting with packaging for the 1400 Series in the late 1950s. In the next series, System/360, IBM chose to follow a unique approach which employed solder joints for the semiconductor connections, allowing ultimately a higher density and total number of interconnections compared to the rest of the industry. This has driven the packaging at the module level to achieve extremely high density and has led to multichip interconnections and multilayers on this first level of package. The dramatically increasing circuit function at the module level requires area arrays of pins to be able to get enough of them in a small area. Thus the next level (second level) of packaging has likewise been driven to provide many layers of dense interconnections to link to the module pins. New types of plated through holes join the many layers of interconnection. The highlights of the technical approaches which have been developed over the twenty-five-year period are discussed briefly in this paper.