Assessing the value of marketing to a business remains a thorny issue in theory and practice. Decision-making at the finance–marketing interface is under-researched, particularly for project businesses. Confronted by demands of accountability concerning the allocation of resources to meet competitive pressures, the paper examines the quality and extent of dialogue in investment decision-making. The return on investment (ROI) and marketing-specific investment (ROMI) are important factors at the marketing–finance interface. ROMI/ROI is examined from quantitative and qualitative viewpoints. The empirical evidence shows that short-term financial criteria dominate and are misaligned to long-term performance of project businesses and business units. Marketing investment in relation to project markets poses a particularly challenging environment. Client lifetime value and programme data sets for ROMI coupled with qualitative decision-making offer ways forward with constructive dialogue at the finance–marketing interface. The paper concludes with detailed recommendations for research and practice. •Paper proceeds with setting out an overview of the ROMI in the framework of project.•ROMI analysis uses the marketing mix and relationship marketing concepts in the project context.•Qualitative research permits understanding the marketing-finance interface in project situations.•Study permits to check the engagement at this interface (acceptance + management).