In this chapter, we discussed the cross-cutting concerns, why those are important, and how the code becomes unnecessarily complex when it is introduced in the application. We discussed AOP to solve the problem of code duplication while using cross-cutting concerns, and how to make it simple using aspects. We discovered many terminologies, such as Advice, pointcut, weaving, and introduction, and how to use them in depth. We also did an integration of logging mechanism as a cross-cutting concern using aspect in the application, using both the schema-based and annotation-based approach. We also discussed introduction advice, which facilitates the addition of new functionalities without changing the original code. We opened the chapter by discussing transaction management, which is another very important cross-cutting concern. However, we haven't talked about it here; the next chapter will be completely dedicated to transaction management.