The product theorem for parametrized topological Reidemeister torsion Wojtek Dorabiala Mark W. Johnson Primary: 19D10; Secondary: 18F25, 19Exx, 55R70 Department of Mathematics Penn State Altoona Altoona, PA 16601-3760 wud2@psu.edu mwj3@psu.edu The goal of this article is to prove the product formula for parametrized topological Reidemeister torsion. The theorem states that the product of the parametrized Euler characteristic of one fibration with the parametrized Reidemeister torsion class of another fibration yields the parametrized Reidemeister torsion class of the product fibration. In the process of establishing the theorem, several new products must be defined involving (derivative theories of) parametrized $\Aof$-theory and a detailed description of the coassembly map for parametrized $\Aof$-theory is included.