Optical systems for data transmission have a history that can be traced back to different roots starting with the invention of the semiconductor laser and the glass fiber in the 1960s. Different application areas such as data center connectivity and long-haul transmission have led to different optical communication solutions. Chip-to-chip communication is a driver for the convergence of these approaches since this is where board-to-board communication and silicon photonics are slated to merge. From the analysis of optical intra-chip and inter-chip systems the required future developments of spectral efficiency, energy efficiency, and packaging can be derived. An overview of the various optical technology options are given in this introductory chapter.