Tendering legislation aims to enhance competitiveness by promoting equality, proportionality, transparency, and non-discrimination. Such legislation applies to the procurement of software packages by public institutions in many countries. This study explores how tendering legislation shapes a buyer's software selection process through the lens of competing decision-making rationalities. From the literature, 3 rationalities enacted in software selection are deduced that we relate to the software selection literature regarding tendering legislation. Through this lens, we subsequently examine how a large health care provider selected a supplier for an electronic health record system after an extensive tendering process. Many health care professionals within this organization were in favour of a particular software package. Yet, the organization purchased a different package from a relatively unknown supplier, the implementation of which failed. The actors involved experienced shaping on 5 decisionmaking themes, the implications of which are evaluated against the functional, economic, and political rationality norms derived from the literature. The findings suggest that compliance with tendering legislation over the public procurement of software results in increased legal complexity, greater linearity and objectivity, more extensive formalization, and less relational communication. Functional norms of rationality are stressed, seemingly to balance the enforced economic norms of rationality and to compensate for the decreased room for political rationality. Even so, the shaping by the tendering legislation threatens functional rationality. Ultimately functional and economic norms of rationality win over political rationality, yet the latter still dribbles through, albeit in a different guise than reported for software selection in general.