  The last decade has seen major progresses in studies of elementary mechanisms
of deformation in amorphous materials. Here, we start with a review of
physically-based theories of plasticity, going back to the identification of
"shear-transformations" as early as the 70's. We show how constructive
criticism of the theoretical models permits to formulate questions concerning
the role of structural disorder, mechanical noise, and long-ranged elastic
interactions. These questions provide the necessary context to understand what
has motivated recent numerical studies. We then summarize their results, show
why they had to focus on athermal systems, and point out the outstanding
questions.
