<p>Curriculum integration is an approach that aims to integrate teaching across traditional subject boundaries. Curriculum integration has received a growing level of interest in recent years in New Zealand, even from secondary schools that up until now have largely retained disciplinary boundaries. However, in spite of this recent popularity, curriculum integration remains a contested concept in terms of its definition, theoretical grounding, and practice, and we still know very little about how and why teachers are enacting this idea.  This study investigated New Zealand secondary school teachers’ perceptions and practices pertaining to curriculum integration. Participants included 25 teachers and senior managers from four New Zealand secondary schools currently employing curriculum integration. A collective case study design was utilised, gathering qualitative data through focus group sessions, semi-structured interviews, classroom observations, and document analysis. The data was analysed thematically.  The findings indicated that teachers’ theoretical understanding of integration was limited, and that most of the programmes were pragmatically founded. Factors that appeared to enhance the success of curriculum integration were the historical roots, whether the programme was initiated by teachers or senior managers, the type and degree of integration employed, if the programme ran as a special curriculum or across the whole school, the level of support received, and the timing of the programmes.  It was apparent that whilst curriculum integration has been advocated by the New Zealand Curriculum, there are still many challenges for secondary schools wishing to employ it. If this is indeed an area of future growth, then the Ministry of Education have a responsibility to provide a clear definition of, and professional development for, curriculum integration. This would help to strengthen the progressive, integrated curriculum espoused in the New Zealand Curriculum so that it is on far less shaky ground than at present.</p>