To improve their competitiveness, companies should acquire the latest software systems. However, many small or medium-sized companies might not be able to afford a proper software acquisition process without the resource and technical support essential for acquiring the right software system. This article proposes a meta-process, software acquisition with an external agent (SAEA), that includes a new industry role, external agent, to substitute for that support.SAEA will significantly reduce the cost of the software acquisition process. For implementing SAEA, the authors also introduce composition trees as a modelling language to collect, integrate, and compare all software requirements from different stakeholders and to identify issues during the software acquisition process. Finally, a real industry case study, for which this process has been successfully implemented, has been provided to illustrate our approach.