It is sometimes suggested that it is inherently impossible to quantify and measure innovation. This article argues that while this is true for some aspects of innovation, its overall characteristics do not preclude measurement of key dimensions of processes and outputs. An important development has been the emergence of new indicators of innovation inputs and outputs, including economy-wide measures that have some degree of international comparability. The article's sections firstly discuss some broad issues in the construction and use of science, technology, and innovation indicators. They then turn (briefly) to the strengths and weaknesses of current indicators, particularly R&D and patents. The final sections of this article cover recent initiatives focusing on the conceptualization, collection, and analysis of direct measures of innovation.