Software reuse is accepted as a source of important benefits, expressed in productivity and quality terms, when an industrial approach is introduced in the software process. However, mainstream software processes such as Unified Process do not include reuse techniques among the tools that software engineers must deal with. In this paper, we present a proposal to introduce software reuse with minimal disturbance of established disciplines by means of the introduction of a new process for product line engineering and the adaptation of Unified Process for specific product construction. This proposal reduces the money and time costs related to the progressive introduction of software reuse in an organization. Some tools that provide support to the process, including a requirement tool and a repository of reusable elements, have been developed.