This book establishes the foundations of the theory of bounded and unbounded weighted
composition operators in L²-spaces. It develops the theory in full generality meaning that the
corresponding composition operators are not assumed to be well defined. A variety of
seminormality properties of unbounded weighted composition operators are characterized. The
first-ever criteria for subnormality of unbounded weighted composition operators are provided
and the subtle interplay between the classical moment problem graph theory and the injectivity
problem for weighted composition operators is revealed. The relationships between weighted
composition operators and the corresponding multiplication and composition operators are
investigated. The optimality of the obtained results is illustrated by a variety of examples
including those of discrete and continuous types.The book is primarily aimed at researchers in
single or multivariable operator theory.
