In order to explain the development of multi-technology companies and industries where several alternative technologies co-exist and interact over long time periods, this paper suggests an extension of path dependency theory by providing a conceptualization of the path notion which incorporates the theoretical possibility of multiple paths and path interaction. The conceptualization is applied to a patent study of three leading companies in the lighting industry: General Electric, Osram/Siemens and Philips. The study shows technology development patterns that are characterized by strong persistence, both within each path and across the whole technology field. These results demonstrate that multiple technological paths can co-exist in companies and industries, characterized by simultaneous long-term presence of several technologies. In such cases, path interaction takes place both between co-existing paths and when new, radically different paths are created. Although further studies are needed to identify the underlying self-reinforcing mechanisms, there is a clear indication that technological path dependency is not restricted to unitary progression patterns, as implied by previous conceptualizations.