Preferential trade agreements are animportant feature of the global trade system. Severalquestions, ranging from the rationale for preferentialarrangements to their impact on members, non-members and thebroader multilateral trade system, are at the forefront ofacademic and policy debates in trade policy. This papercontributes to the literature in two ways. First, itpresents a new database that offers a detailed assessment ofthe content of preferential arrangements, examining thecoverage and legal enforceability of provisions. Thedatabase covers 279 agreements signed by 189 countriesbetween 1958 and 2015, which reflects the entire set ofpreferential trade agreements in force and notified to theWorld Trade Organization as of 2015. Second, the paperpresents some novel stylized facts on preferentialarrangements based on the analysis of the data. The keyinsight is that preferential trade agreements became deeperover time. A growing number of these treaties cover anextended set of policy areas, frequently with legallyenforceable provisions, in areas under the current WorldTrade Organization mandate and in four leading areas outsidethe current World Trade Organization mandate: competitionpolicy, investment, movements of capital, and intellectualproperty rights protection. Accounting for the changingcoverage of preferential trade agreements, that is, their“horizontal depth,” is essential to gain a more complete andaccurate understanding of where the global trading system isgoing and how its governance can be improved.