A team of theoretical physicists from the Physical and Mathematical Sciences Department (SPM) of CNRS, joined the IAP in 2001. Together they made up a research group called “GReCO” (Gravitation and cosmology), under the label Formation de recherche en evolution - “Evolving research group” (FRE2435). These physicists are specialists of primordial cosmology and gravitation, and their research themes are complementary to those traditionally studied in astrophysics and observational cosmology, within labs attached to the Sciences of the Universe Department (INSU).

In 2001, the IAP joined the Université Pierre et Marie Curie (Paris 6) and became a mixed research unit, UMR7095.

In 2005, Laurent Vigroux became the IAP’s new director. The IAP and the GReCO merged into a single CNRS-UPMC Mixed Research Unit (UMR 7095).
Research teams were re-organised into six groups:

• Theoretical Physics: Gravitation and Cosmology;
• Large-scale Structure and Deep Universe;
• Cosmology and High-Energy Astrophysics;
• Origin and Evolution of Galaxies;
• Stellar, Planetary and Extrasolar Planetary Physics;
• Exoplanets and the Interstellar Medium.

By decree on November 30th 2005, the IAP was granted the status of Observatoire des Sciences de l’Univers (“Observatory for the Sciences of the Universe”) and Ecole Interne (“Internal school”) of the Université Pierre et Marie Curie. By ministerial decree on November 24th 2006, Laurent Vigroux was named director of the Observatoire Institut d’Astrophysique de Paris of the Université Pierre et Marie Curie, for a five-year term.