**4. Summary**

OI has been a strong application tool in almost every discipline of science and engineering. As devices based fundamentally on the superposition of light and all-optical, noninvasive signal processing, these methods have remarkable flexibility and relevance. In this chapter, an overview of the most recent applications has been presented. While typical applications in science and engineering research have seen remarkable updates in the past few years, some novel applications have also emerged as a result of collaborative efforts in cross-disciplinary projects.
