"Research and experimental development (R&D) comprise creative and systematic work undertaken in order to increase the stock of knowledge – including knowledge of humankind, culture and society – and to devise new applications of available knowledge."

To qualify as R&D, the following elements need to be present in the working process: novelty, creativity, uncertainty, systematic approach,and being transferable and/or reproducible.

Furthermore, the term 'R&D' covers three types of activity: basic research, applied research and experimental development.

MERI collects longitudinal data concerning research personnel and research expenditure in Belgium divided in four different sectors: the business enterprise sector (BES), the government sector (GOV), the higher education sector (HES) and the private non profit sector (PNP).

From 2021 onwards, two important methodological changes were introduced. They are the result of international agreements at the European level (EUROSTAT) and within OECD working groups.

First, for the enterprise sector (BES), data are now available at two levels of aggregation. Up until 2020, the legal unit, which corresponds to the VAT number, has always been the statistical unit used for all business statistics. Due to the increasing globalisation of economic activities and the ensuing emergence of larger business entities, an additional unit of aggregation has been created: the enterprise unit. This statistical unit should be considered as an intermediate level between the legal unit and the corporate group structure. An enterprise unit consists of legal units that cooperate intensively and make use of common business entities for certain operational, administrative, or financial activities. A legal unit is the smallest unit with legal accountability, an enterprise unit comprises several legal units, which in turn may be part of a larger corporate structure with a foreign decision centre and one or more subsidiaries around the world.

This new aggregation level only impacts a limited number of statistics: all data broken down by NACE codes and size classes are affected, but all other data remain unchanged.

The second change impacts personnel data for all sectors, which include from 2021 onwards an additional category of collaborators. Previously, R&D personnel statistics only related to internal personnel, i.e. employees on the payroll of the company or organisation. Data collected in 2021 will for the first time also include persons hired by the R&D performing unit to work under its supervision on its internal R&D activities, but who are not employees of the company or organisation. This category is defined as external personnel.