Since 1996 ESA and NASA, along with the Canadian Space Agency, have collaborated on designing and constructing the James Webb Space Telescope (JWST), widely considered as a follow-up mission to the hugely successful Hubble Space Telescope.

ESA's participation in the JWST mission was formally approved by the ESA Science Programme Committee in 2003. The four major European contributions to the mission are formalised in the Memorandum of Understanding on JWST signed by NASA and ESA in 2007:

• provision of the NIRSpec instrument;
• provision of the Optical Bench Assembly of the MIRI instrument through special funding from the ESA member states;
• provision of the Ariane-5 ECA launcher;
• manpower support to JWST operations.

In return for these contributions, ESA gains full partnership in JWST and secures full access to the JWST observatory for astronomers from Member States on identical terms to those of today on the Hubble Space Telescope. European scientists will be represented on all advisory bodies of the project and will be expected to win observing time on JWST through a joint peer review process, backed by an expectation of a minimum ESA share of 15% of the total observing time.