The architecture of the project rests on four building blocks. Block one consists of three work packages-the philosophical foundations of a fair system of DI (WP1), legal feasibility and constitutional acceptability of DI (WP2) and what citizens, governments and parties want from DI (WP3). Work on W1 and 2 is critical to the project as it establishes the criteria for building and assessing scenarios which is the culmination of the project. WP3 is path breaking as our knowledge on what citizens, governments and parties want of DI is fragmentary and limited. The focus in this period was on the design of templates and survey experiments for data collection. Block 2 focuses on the patterns, causes and effects of DI (WP4). In RP1, the main task in WP4 was on updating and expanding the EUDIFF1 and EUDIFF2 datasets on primary-law and secondary-law differentiation, respectively. Both datasets were updated for the time-period including 2018. In addition, in cooperation with the partner from the Liechtenstein Institute, the selective adoption of EU secondary law in the EFTA countries (EEA and Switzerland) was included in the EUDIFF2 dataset. Block 3-zooming in- consists of four WPs, internal differentiation (WP5), external differentiation (WP6), differentiated implementation (WP7) and alternatives to DI (WP8). Case studies are an essential component of InDivEU as they enable us to zoom-in on DI in relation to particular policies or geographic areas. In RP1, WP5 on core state powers focused on two case studies, the Schengen system and the Common Foreign and Security Policy (CFSP). These cases relate to the borders of the Union and its actions beyond the EU territory. On Schengen, detailed data was collected on two important EU agencies, the European Border and Coast Guard Agency (FRONTEX) and the European Asylum Support Office (EASO). This included data on the regulation of the agencies, their budgets, equipment and staffing profiles. The work on the CFSP analysed the European Defence Agency (EDF) from its establishment in 2004 to 2019 and the 37 civilian and military missions undertaken by the EU from 2003 to 2019. WP6 offers a series of case studies on the relationship between the EU and its neighbours, notably the European Free Trade Association (EFTA) states, Turkey and the UK. The decision by the UK to exit the EU has brought the dynamic of external differentiation sharply into focus as the EU and UK work out their future relationship following 47 years of membership. A distinctive element of the InDivEU project is to assess alternatives to DI. WP7 is developing a dataset on differentiation through flexible implementation. The codebook for data gathering is complete and work has begun on the completion of the data set. WP8 adopts the lens of experimental governance and conducted case studies on EU energy regulation, genetically modified organisms (GMOs) and EU financial regulations during this RP. Block 4 on synthesising and designing scenarios for DI comes in the latter half of the project.