-------------------------------------------------------------------------- `M2-Brane Theories and Marginal Deformations' Abstract: I will review various aspects of recently proposed effective descriptions of stacks of M2-branes. The corresponding theories are Chern-Simons-matter theories with product gauge group. They are to be seen as the M-theory analogue of super Yang-Mills theory, which provides an effective description of D-branes in string theory. I will focus particularly on marginal deformations of these M2-brane theories and the resulting conformal infrared fixed points. --------------------------------------------------------------------------