Semiconductor optical amplifier (SOA)-based functional devices are of interest for optical signal processing due3 to their many attractive features, which include high-speed operation, potentially low polarization dependency, large optical bandwidth and low loss. Furthermore, they may be integrateable and have a moderate to low power consumption. The fact that SOA-based devices can be used for a multitude of purposes and either have the above-mentioned characteristics inherently or can be fabricated to accommodate them, makes them prime candidates for the implementation of a variety of functionalities. Among others, SOAs are attractive as fast optical gates, where one of their most significant features is a high on-off ratio, which is critical for cross-talk suppression. Furthermore, SOAs employed as nonlinear elements, either alone or in interferometers, have demonstrated the capability of more complex functionalities such as wavelength conversion, switching, time-division (de)multiplexing as well as 2R and 3R regeneration. Additionally, more exotic functionalities such as Boolean logic gates can be realized, making SOA- based devices attractive for use in a broader system or network perspective. In this paper, the focus will be on techniques for wavelength conversion, 2R and 3R regeneration employing cross-phase modulation in interferometers, which have demonstrated some of the most promising results. Furthermore, the implementation of all-optical logic using SOA-based interferometers will be discussed, and some of the novel employments of these functionalities will be presented.