Michel Chipot 
Handbook of Differential Equations: Stationary Partial Differential Equations [PDF ebook] 

A collection of self contained state-of-the art surveys. The authors have made an effort to achieve readability for mathematicians and scientists from other fields, for this series of handbooks to be a new reference for research, learning and teaching. — Written by well-known experts in the field- Self contained volume in series covering one of the most rapid developing topics in mathematics- Informed and thoroughly updated for students, academics and researchers