Jean-Louis Loday and Bruno Vallette
You can download the whole book for the next few weeks at the following
pdf file (December 2010, 512 p.).
The reference for the version 1.00 is as follows:
J.-L. Loday and B. Vallette, Algebraic operads, Grundlehren Math. Wiss.
346, Springer, Heidelberg, 2012.
What you will find in the book:
-- A modern treatment of Koszul duality for associative algebras, where
algebras and coalgebras are put on the same footing (Chapters 2-3-4).
-- The basics of symmetric operads and nonsymmetric operads (Chapter
-- Koszul duality for algebraic operads (Chapter 6-7-8)
-- The example of the associative operad, including A-infinity algebras
-- Applications of the Koszul duality of operads to homotopical
algebra, including the Homotopy Transfer Theorem (Chapter 10-11-12).
-- Many examples (Chapter 13).
Most of these parts can be read independently, see Leitfaden
of Jean-Louis Loday,