The paper compares Marx's treatment of financial and merchant capital in the 1861-63 Manuscripts and in Capital, Vol. 3. A major focus is on the characteristics that distinguish the capitalist from the pre-capitalist versions of these forms of capital. The paper also traces the evolution of Marx's views on: (1) the financial system's role as unifying individual capitals into one system and (2) the development of different forms of credit, including credit money.