This entry is about the article
Grothendieck Festschrift, vol. II,
Birkhäuser Progress in Math. 87 (1990) pp.111-195.
The main theorem is a Tannakian reconstruction theorem, which repairs a problem in the book
which had a substantial gap in the proof of the main theorem.
At the end of the article there is an application to the differential Galois theory (which has been earlier much studied by A. R. Magid) which is the Galois theory for differential rather than algebraic equations.
In the followup
the conditions for Tannakian reconstruction are relaxed further, see at Deligne's theorem on tensor categories.
Generalization to “non-neutral” Tannakian categories, and representations of gerbes is in