This thesis explores learning outcomes (LOs) as a prominent policy and feature of European higher education (HE) reforms. Widely used to describe the learning expected at different levels of education, LO's emerging role in degree-level practices is explored via interviews with teachers, leaders, and students, from eight degree-programme cases at English and Norwegian universities. These evidence LOs being interpreted and used in planning, teaching, learning and management. The four publications included in this thesis provide detailed accounts of LO practices on various levels, in applications spanning course development, teaching reform and quality assurance. LOs are shown to influence practice, disputing views of them as a purely symbolic or formal policy. However, their application and influence are complex and ambiguous. They can support clear, constructive approaches to planning and teaching, but are also perceived as a problematic, potentially counter-productive way to communicate about learning. Their role in management is still emerging, but they appear to create new opportunities for oversight and steering of teaching, and their growing role in quality assurance seems to create pressure for the development of more specific, measurable LOs. The analysis highlights the challenge of reconciling flexible, open 'process' forms of LOs developed for teaching with concrete, measurement-focused 'product' LOs needed for oversight or comparison applications. The enactment process presented here is incompatible with simple 'top down' or 'bottom up' perspectives on policy formation, evidencing local adaptation and variety, and examples of highly standardised or rule-based practices. An argument is developed that explaining these findings requires a deliberate engagement with the mess and multiplicity which characterise LOs. A set of metaphors are developed to offer an alternative view of LOs as policy nets, knots and tangles. These convey multiplicity and complexity, while offering new ways to look at relationships between divergent LO forms and practices, explanations for the enactment processes identified, and a way to highlight the key choices HE actors and policy makers confront as they continue to enact LOs in universities.