Context: Requirements engineering (RE) for software products offered to a mass market is concerned with deciding which of the diverse and large amounts of potential requirements to implement into future releases of a product. While being the key for achieving success, these decisions are very complex. Therefore, the need for decision support is well acknowledged. However, despite a growing body of research in this area, software companies are still experiencing problems in making informed decisions on which requirements to include in the software, or knowing how to maximize the potential ROI of a software release. Objective: The purpose of this thesis is to provide an increased understanding of how better decisions regarding the content of software products can be achieved. The research addresses two currently unresolved areas: balancing investments in different requirement types (commercial requirements, internal quality aspects and innovations) and identifying reasonable requirement analysis effort for informed requirements selection decisions. In order to address these areas the thesis focuses on investigating: 1) how uncertainty in the value proposition of a requirement is influencing the balance between investments in different requirement types; and 2) challenges and opportunities introduced by agile practices to RE decisions. Method: The presented research has an exploratory character and consists of empirical studies conducted both in industrial and academic settings. Results: The results include findings from an academic experiment and an industrial case study indicating that commercial requirements will be preferred over innovations and internal quality aspects. This is because innovations and internal quality aspects are associated with higher uncertainty in their value offering compared to commercial requirements and thereby are perceived to have higher level of business risk. The thesis also offers findings from an industrial case study, showing a misalignment between agile principles and the ability to take informed release planning decisions. Further, a framework (NORM) for finding an appropriate balance between information needs of RE decisions and requirements analysis effort is suggested. Conclusions: Uncertainty associated with the value proposition of different requirement types influences the requirements selection decisions, resulting in a dominance of commercial requirements. Thus, in order to achieve a better balance between investments in commercial requirements, internal quality and innovation it is important that uncertainty in the value offering of requirements is explicitly managed by methods providing support for RE decisions in a market-driven context. Agile methods provide opportunities to minimize overhead caused by excessive analysis of requirements, however adopting agile approaches in their current form pose challenges for performing product management and taking informed RE decisions in a market-driven context. Therefore, a balance between agility and information needs of RE decisions must be found. In combination, the thesis results offer a new insight and form a ground for defining improved approaches for supporting requirement selection decisions.