This paper discusses some methodologies for estimating potential output and the output gap that have recently been studied at the Bank of Canada. The assumptions and econometric techniques used by the different methodologies are discussed in turn, and applications to Canadian data are presented. The first group of methods considered are those that simply use some implicit or explicit assumptions about the dynamics of real output to identify the output gap, including the Hodrick and Prescott filter for identifying the cyclical component of output. The second group consists of approaches that combine their assumptions with information from assumed or structural relationships between the output gap and other economic variables. The third class of methods uses multivariate rather than univariate dynamic relationships, often in combination with structural relationships from economic theory, to estimate output gap as a particular transitory component of real output.