  Algebraic quantum field theory is considered from the perspective of the
Hochschild cohomology bicomplex. This is a framework for studying deformations
and symmetries. Deformation is a possible approach to the fundamental challenge
of constructing interacting QFT models. Symmetry is the primary tool for
understanding the structure and properties of a QFT model.
  This perspective leads to a generalization of the algebraic quantum field
theory framework, as well as a more general definition of symmetry. This means
that some models may have symmetries that were not previously recognized or
exploited.
  To first order, a deformation of a QFT model is described by a Hochschild
cohomology class. A deformation could, for example, correspond to adding an
interaction term to a Lagrangian. The cohomology class for such an interaction
is computed here. However, the result is more general and does not require the
undeformed model to be constructed from a Lagrangian. This computation leads to
a more concrete version of the construction of perturbative algebraic quantum
field theory.
