The purpose of this research was to elicit baseline data about Irish post-primary teachers’ conceptions of assessment. Post-primary education in the Republic of Ireland is currently in the midst of significant curriculum and assessment reform at Junior Cycle, the first three years of the secondary school system. Central to this change is the positioning of the teacher at the heart of the assessment process. The successful implementation of the new assessment practices will not only require a high level of teacher assessment literacy, but will also depend upon the extent to which teachers’ conceptions of assessment align with the philosophical underpinnings of the reform. Research has indicated that teachers’ beliefs serve to filter information entering the cognitive domain, to frame particular educational situations or problems and to guide teachers’ intentions and actions (Fives & Buehl, 2012). In light of this evidence, the introduction of new assessment initiatives should take account of how teachers conceive of the nature and purpose of assessment. Adopting a non-experimental crosssectional design, this study surveyed a large sample (n=489) of post-primary teachers using the abridged version of Brown’s (2006) Teachers’ Conceptions of Assessment Inventory (TCoA-IIIA). This 27-item self-report instrument is designed to elicit teachers’ level of agreement with four intercorrelated assessment factors (i.e., school accountability, student accountability, improvement and irrelevance). Quantitative data derived from the survey were analysed using a mixture of descriptive statistics, exploratory factor analysis, independent samples t-tests and one-way analysis of variance. Maximum likelihood exploratory factor analysis resulted in a 5-factor solution for the Irish data which differed somewhat from Brown’s (2006) original model. Implications of the results for the conceptualisation of assessment in the Irish post-primary context are considered.