Recommended textbooks for Hamiltonian group actions? I am doing a project on Hamiltonian group actions on symplectic manifolds, and my supervisor was able to list several good books on Riemannian geometry to start me off, but he didn't know of any single place to learn about Hamiltonian groups. 
I have found some books (even available online from the author!) that come highly recommended, specifically: Introduction to Symplectic and Hamiltonian Geometry, A. C. da Silva.
As the title suggests however, this seems to come from more of a geometric standpoint. Which books are recommended that might focus on the group-theory and topology end of this subject? The project description specifically mentions cohomological obstructions, something that I think is related to group cohomology? (At this point I'm getting all of this from Wikipedia...) 
I have had basic, introductory courses in Differential Geometry (in $\mathbb{R}^n$) and in topology (up to calculating the first fundamental group of a topological space). 
Thank you in advance for any input!
 A: The best Book about Hamiltonian action is
Moment Maps, Cobordisms, and Hamiltonian Group Actions
 Par Victor Guillemin,Yael Karshon,Viktor L. Ginzburg
The second excellent lecture note is from  Heckman
Lecture notes on Geometry of the momentum map, written with Gert Heckman,
Moreover, from geometric point of view this book is excellent
Convexity Properties of Hamiltonian Group Actions 
 Victor Guillemin,Reyer Sjamaar
Following note is also good and introductory 
Hamiltonian group actions, Sara Grundel
Also the master thesis entitled "The Momentum Map, Symplectic Reduction and an
Introduction to Brownian Motion" which supervised by Alan Weinstein is very good 
And in final if you know french as Francois said , Structure des systèmes dynamiques
A: The project is now finished, and for anybody else looking to do something similar, I would like to add the following book as an excellent source for an introduction to the material:
An Introduction to Symplectic Geometry, Berndt
This was found more helpful than any of the others, (save perhaps da Silva's lectures) as a short-term introduction to the subject.
