Abstract The information and communication technology (ICT) industry has expanded rapidly during the past decades and has changed in terms of frequent technology development, increase in product complexity, constant time-to-market pressures, heavy price erosion and the decrease in physical dimensions. Successful product development thus requires effective requirements engineering and acknowledging the different needs of internal and external stakeholders. A vital challenge for ICT companies is requirements for products typically changing during product development. In addition, requirements are not interpreted the same way in different parts of organisations. Today’s products being more complicated than ever, and customer segments more fragmented, requirements engineering and testing is currently a bottleneck for product development and production. In this dissertation, requirements engineering in ICT companies is studied from four complementary viewpoints – current challenges, manufacturing requirements, external requirements, and optimal acceptance limits in manufacturing. The dissertation is qualitative and inductive in nature and is based on interviewing experienced industrial managers. The study included also an element that can be seen as constructive. The researcher has analysed the obtained material and made conclusions. The main result of this dissertation can be summarised as requirements engineering having a coordinating role in complex ICT product development. In addition, this study highlights the potential of the design for excellence (DfX) concept for addressing a vast amount of requirements from numerous internal and external stakeholders. ICT companies should consider full integration of tools and databases related to requirements. Also, delaying decision-making in product development projects to a stage, where adequate amount of information is available, could help coping with changing requirements. Addressing the challenges of a large and complex organisation requires creating and documenting processes for a vast amount of issues. It may be sensible to consider the benefits of establishing a separate DfX management organisation for coordinating internal and external requirements. In addition, the managers in ICT companies should notice that in contrast to the conventional thinking, widening the manufacturing acceptance limits makes business sense in some cases.