This essay is about two properties that some theories of physics have — determinism and locality — and the gaps that can exist between how they are understood as properties of physical reality, how they are understood as properties of mathematical theories, and how they are formally defined as properties of mathematical theories. I will point out one such gap that seems to have gone widely unremarked, and that could admit an interesting class of physical theories. On the other hand, for readers already well acquainted with Bell's Theorem, it may be helpful to know up front that, ultimately, I will identify a particular class of mathematical theories that have a sort of locality —mathematical locality, but not apparently physical locality— but that do not satisfy the assumptions of the Theorem and therefore are not constrained by Bell's Inequality (and no, this is not related to Joy Christian's work; I'm going to take an orthodox view of Bell's Theorem).
Abstract: Algebraic quantum field theory provides a general, mathematically precise description of the structure of quantum field theories, and then draws out consequences of this structure by means of various mathematical tools -- the theory of operator algebras, category theory, etc.. Given the rigor and generality of AQFT, it is a particularly apt tool for studying the foundations of QFT. This paper is a survey of AQFT, with an orientation towards foundational topics. In addition to covering the basics of the theory, we discuss issues related to nonlocality, the particle concept, the field concept, and inequivalent representations. We also . 202 pages; to appear in Handbook of the Philosophy of Physics