April through November of 1912 saw Bertrand Russell closely collaborating with Wittgenstein on a joint philosophical program. Wittgenstein’s meeting with Gottlob Frege in December that year, however, prove to be something of a watershed and put an end to the collaboration and to the project. The present chapter outlines, in Sect. 2.1, the key elements of the abandoned joint program, foregrounding what each of them contributed to it. Section 2.2 spells out what exactly about was the program that Frege criticized in a way that led Wittgenstein to break with Russell. Building upon the findings of the first two sections, the third recasts along previously undeveloped lines the logical/philosophical insights that Wittgenstein introduced and applied in the two years following his fateful encounter with Frege. The chapter concludes with an overview, in Sect. 5, of the transformative consequences for Russell’s philosophical thinking that are directly attributable to Wittgenstein’s Frege-inspired critique of the erstwhile joint program.