  This article is a survey of algebra in the $\infty$-categorical context, as
developed by Lurie in "Higher Algebra", and is a chapter in the "Handbook of
Homotopy Theory". We begin by introducing symmetric monoidal stable
$\infty$-categories, such as the derived $\infty$-category of a commutative
ring, before turning to our main example, the $\infty$-category of spectra. We
then go on to consider ring spectra and their $\infty$-categories of modules,
as well as basic constructions such as localization, completion, and
dualizability. We conclude with a brief account of the cotangent complex and
deformation theory.
