In the first article, Martin Ravallion (Georgetown University) reviews the Luxembourg Income Study ( _LIS),_ produced by the LIS Cross-National Data Center in Luxembourg. A comment by Gornick, Jäntti, Munzi and Kruten follows. François Bourguignon (Paris School of Economics) reviews two databases concerned exclusively with Latin America: CEPALSTAT, produced by the Economic Commission for Latin America and the Caribbean; and the Socio-Economic Database for Latin America and the Caribbean (SEDLAC), produced by the Center for Distributive, Labor and Social Studies (CEDLAS) at Universidad Nacional de La Plata, in partnership with the World Bank. Leonardo Gasparini and Leopoldo Tornarolli (Universidad Nacional de la Plata) review the OECD’s Income Distribution Database (IDD). Tim Smeeding and Jonathan Latner (University of Wisconsin – Madison) review the World Development Indicators/PovcalNet, produced by the World Bank; and All the Ginis (ATG), produced by Branko Milanovic of the City University of New York. Stephen Jenkins (LSE) reviews the _World Income Inequality Database (WIID)_ , produced by UNU-WIDER; and the _Standardized World Income Inequality Database (SWIID)_ , produced by Frederick Solt, of the University of Iowa. A short note by Martin Wittenberg (University of Cape Town) on South African data in the SWIID follows and comments by Badgaiyan, Pirttilä and Tarp (WIID) and Solt (SWIID) conclude.

At the outset, reviewers were provided with a set of common guiding questions, as well as with a description of the databases and a master data set with all the inequality indicators organized by country, data source and year. We asked authors to comment, in particular, on the accessibility and user-friendliness of the databases; the quality of the documentation; the reliability and accuracy of reported indicators; and the transparency and replicability of how data was calculated and presented.

During the course of preparation of this special issue, a number of the data sets have been updated. We have therefore made every effort to ensure that the reviews specifically note which versions they discuss or the date on which the data was accessed and we do the same in this introduction. Unless otherwise noted, the methodologies we describe and the statistics that we present are based on the versions of the data sets available online in November 2014. In some cases, the summary statistics included in this Introduction come from a more recent version of the data set than the version that received a full review. Most notably, our discussion of WIID refers to WIID V3.0B which incorporates many of Jenkins’ (2015) suggestions for improvement (Badgaiyan et al., 2015).

Although our review covered most of the existing international databases, we make a special note of five that have not been included: _Commitment to Equity_ (CEQ), the _World Top Incomes Database_ (WTID), the _GINI Project_ , the _Global Consumption and Income Project_ (GCIP) and the _University of Texas Income Project_ (UTIP). Although they are not reviewed in separate articles in this special issue, this should not be taken as a judgment on their quality or relevance, and we will occasionally refer to them below.

The remainder of this Introduction is organized as follows. Section 1 presents a brief description of the eight databases, and classifies them into three broad groups. We summarize the main methodological differences between the data sets in Section 2. In Section 3, we briefly discuss the extent to which inequality levels and trends differ across databases. We conclude with an overall assessment and some advice for users of these databases.

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