This paper presents new research on the institutionalization and authority of international parliamentary institutions (IPIs). We seek to contribute to the research on transnational representation by proposing new empirically-based theories on the conditions under which IPIs emerge and deepen their authority. In order to do so we propose a definition of IPIs and conceptualize three dimensions along which they vary in nature: constitutional status, institutional authority and institutionalization. Based on these concepts we design the collection of a time series cross sectional database of 60 IPIs, of which we discuss the operationalization and show selected descriptive results.