The scope of this chapter is to investigate the critical factors for the success of stock brokerage processes via the Web, using financial portals on the Brazilian Internet, from the perspective of the investor. The framework of the online stock trading system is presented in order to compare the traditional form of stock brokerage with that made possible by the Internet and discuss some of the issues regarding intermediation and disintermediation that has occurred in the process. Conclusions are drawn based on a survey conducted with Brazilian investors who operate using Internet stockbrokers for the intermediation of their stock operations. The findings were analyzed from the perspective of the theoretical reference framework created and outlined here. Critical aspects for the success of stock brokerage over the Internet, from the investor’s standpoint, were assessed and presented, while areas for further research were also identified.