Algebraic stacks

Algebraic stacks are the geometric objects on which we will consider our D-modules and quasi-coherent

sheaves. For that reason it's necessary to know what they are. Below are some suggestions for the 

reading: 

1) The original paper by Deligne and Mumford, Sect. 4 

2) "Champs algebriques" by Laumon and Moret-Bailly

3) Chapter 1 by A. Vistoli in the book

4) Notes by Dennis Gaitsgory and Toly Preygel