Operads, homotopy algebra and iterated integrals for double loop spaces
  This paper provides some background to the theory of operads, used in the first author's papers on 2d topological field theory (hep-th/921204, CMP 159 (1994), 265-285; hep-th/9305013). It is intended for specialists. 
Ezra Getzler and J. D. S. Jones