  In this dissertation, we study the generalized symmetries in supergravities
and superconformal field theories from the string theory perspective.
  Part one is devoted to the study of string universality in high spacetime
dimensions. Answering this question requires us to combine the following two
approaches. In the "top-down" approach, We focus on supergravity theories in 7,
8, and 9 dimensional spacetime with 16 supercharges. We emphasize two discrete
aspects of these theories: generalized global symmetries and frozen
singularities. We give an exhaustive classification of IIB supergravity theory
in 8D, particularly emphasizing these two discrete aspects. In the "bottom-up"
approach, we present a consistency condition of general 8D supergravity
theories involving their higher-form symmetries use it to rule out many global
structures of the gauge groups in 8D supergravity theories that do not admit
string theory constructions. Part two studies the generalized global symmetries
of geometrically-engineered quantum field theories via string theory. We
examined branes wrapping on relative topological cycles that give heavy defects
that are charged under generalized global symmetries, which can then be used to
construct new lower-dimensional theories. By investigating the string theory
origin of the topological operators, we provide a general construction of these
topological operators in the context of geometric engineering as branes wrapped
on the homological cycles in the asymptotic boundary of the internal geometry.
We illustrate this proposal by determining non-invertible 2-form symmetries in
6D superconformal field theories. Furthermore, by wrapping type IIB 7-brane on
the entire asymptotic boundary of the internal manifold, we explicitly give a
unified string-theoretic construction of two different types of field-theoretic
non-invertible duality defects.
