The evolution of European Union law: A new data set on the Acquis Communautaire
| Published date | 01 December 2019 |
| Date | 01 December 2019 |
| Author | Joshua C Fjelstul |
| DOI | 10.1177/1465116519842947 |
| Subject Matter | Forum |
Article
The evolution of
European Union law:
A new data set on the
Acquis Communautaire
Joshua C Fjelstul
Department of Political Science, Emory University, Atlanta,
GA, USA
Abstract
The European Union legal system is one of the most complex and sophisticated in the
world. This article models the Acquis Communautaire (i.e. the corpus of European Union
law) as a network and introduces the Evolution of European Union Law data set, which
tracks connections between European Union primary law, European Union secondary
law, European Union case law, national case law that applies European Union law, and
national law that implements European Union law. It is the largest, most comprehensive
data set on European Union law to date. It covers the entire history of the European
Union (1951–2015), contains over 365,000 documents, and records over 900,000
connections between them. Legislative and judicial scholars can use this data set to
study legislative override of the Court of Justice of the European Union, the imple-
mentation of European Union law, and other important topics. As an illustration, I use
the data set to provide empirical evidence consistent with legislative override.
Keywords
Acquis Communautaire, European Union law, legislative override, network data
Corresponding author:
Joshua C Fjelstul, Department of Political Science, Emory University, 1555 Dickey Drive, Atlanta,
GA 30322, USA.
Email: joshua.fjelstul@emory.edu
European Union Politics
2019, Vol. 20(4) 670–691
!The Author(s) 2019
Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/1465116519842947
journals.sagepub.com/home/eup
The European Union (EU) legal system is one of the most complex and sophisti-
cated in the world. The Acquis Communautaire (i.e. the corpus of EU law) encom-
passes multiple international treaties, well over 100,000 legislative acts, and tens of
thousands of court rulings. Unlike other international legal orders, the EU legal
system is deeply integrated with the domestic legal systems of member states.
National courts interpret and apply EU law in domestic litigation, and national
parliaments enact legislation to transpose EU law into national law.
This article models, for the first time, the vast network of legal instruments that
constitute the Acquis Communautaire and introduces the Evolution of European
Union Law (EvoEU) data set, which records the structure of the network. The
data set covers the entire history of the EU (1951–2015). It tracks over 900,000
connections between over 365,000 EU legal instruments across five domains of EU
law: EU primary law (e.g. treaty articles), EU secondary law (e.g. directives, reg-
ulations, and decisions), EU case law (e.g. judgments by the Court of Justice,
judgments by the General Court, and advocate general (AG) opinions), national
case law that refers to EU law, and national law that implements EU law. These
connections capture legislative and judicial outcomes that scholars are interested
in, such as amendments to secondary laws, decisions regarding documents in court
rulings, actions by national governments and courts to implement and apply EU
law, and citations between legal instruments.
Legislative and judicial scholars will see many uses for this data. Due to space
constraints, I focus on how scholars can use the data to study the relationship
between the legislative and judicial processes. I present a brief research application
that uses the EvoEU data set to show that member states are more likely to amend
laws that have been interpreted by the Court of Justice of the European Union
(CJEU), which indicates a feedback loop between the legislative and judicial pro-
cesses consistent with legislative override—attempts by member states to constrain
the Court by amending secondary laws that the Court has interpreted (Carrubba
et al., 2008; Larsson and Naurin, 2016; Martinsen, 2015).
The primary empirical challenge to studying big-picture questions about the
development of EU law is a lack of comprehensive data on the network of EU
legal instruments that scholars can use to establish stylized facts and test theory.
Recently, there have been a number of important data-collection efforts related to
EU law, but these efforts, while overlapping in some cases, are largely uncoordi-
nated (Carrubba and Gabel, 2015; Derle
´n and Lindholm, 2014; Frankenreiter,
2018; H€
age, 2011; Hu
¨bner, 2016; Larsson and Naurin, 2016). This article addresses
this challenge by introducing the EvoEU data set.
The data set contributes to the empirical study of EU law (a) by providing
scholars with a comprehensive picture of how the many facets of EU law relate
to each other and (b) by providing a framework for future data collection.
Successful scientific cumulation in the study of EU law will depend on the
public availability of comprehensive, compatible data sets that scholars can
easily use and build on (Gabel et al., 2002). The EvoEU data set draws on raw
metadata from EUR-Lex, the EU’s official archive of legal instruments. It contains
Fjelstul 671
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