Data is useful for classifying, ordering and quantifying international phenomena. The practical dimension of representing reality through figures and the power of objectification of data explain why databases are numerous and data is often used in international relations research. However, one cannot use figures rigorously without also embracing a qualitative approach to data, taking into account the way data is constructed. Knowing who has put together the data, how and for what purpose is an essential prerequisite for all research. Attention to the definitions chosen and the methodologies employed is crucial, as illustrated through the focus on databases and composite indicators dealing with conflict and peace. More generally, this chapter demonstrates the value of a critical "de-constructivist" stance toward data.