lanar processes to manufacture electronics and optical components. The first part of the chapter is devoted to optical planar components built on the III-V platform. The most important of those components is the semiconductor laser, both for the huge number of telecom and non-telecom applications and for the key role it plays in telecom equipments. We will not try to make a survey of the semiconductor laser technology per se, but we will only summarize the characteristics and the main evolution potentialities of the devices used in telecommunications. These devices are essentially signal sources or pump lasers for fiber amplifiers and we will consider both the applications, which require quite different devices. We will add here also a brief description of the linear characteristics of semiconductor optical amplifiers (SOAs), which will be considered for the potentialities related to their nonlinear behavior in Chapter 10. After a brief analysis of the modulators, both from III-V materials and from lithium niobate (LiNbO3), the first part of the chapter devoted to planar optics comes to an end. In the second part of the chapter we will analyze the impact of electronic evolution on telecommunication equipments. Electronics is by far the most important technology used in telecommunication equip- ments and modern telecommunications would be unconceivable without very large-scale integrated circuits. Naturally it is not possible to make a review of electronics technology from first prin- ciples, and we will assume that the reader has already a familiarity with basic electronics principles and potentialities. Thus only the most recent electronic development that has an impact on telecommunica- tions will be reviewed, excluding wireless technologies, both traditional radio bridges and wireless access in all its different standards. After a brief review of the evolution of the complementary metal oxide semiconductor (CMOS) transistors, the base element of electronic circuitry, the discussion on electronics is divided in