A high rate of absence of teachers from their posts is a serious obstacle to delivery of education in many developing countries, but hard evidence on the problem has been scarce. This study, carried out as part of a new multi-country survey project, is the first systematic investigation in Peru into the extent and causes of teachers' absence from schools. Data from our nationally representative survey of public primary schools, based on unannounced visits and direct observation of teachers, reveals that public school teachers in Peru are absent from their posts 11 percent of the time. While this overall absence rate is low compared with those of other survey countries, the absence rates in Peru's poorest and remotest communities are much higher--16 and 21 percent, respectively. In our multivariate analysis of the causes of public school teacher absence, we identify several important variables that are associated with increased absence: poor working conditions, such as poorer communities and infrastructure; teachers with fewer ties to the school's community; contract teaching; and, perhaps, an absence of private competition. By contrast, proxies for more vigorous top-down and bottom-up monitoring are not associated with lower absence. These results, together with the relatively high overall public school teacher attendance rates in an environment where financial incentives for performance are weak, suggest that non-pecuniary incentives are important determinants of teacher performance.