As your familiarity with LaTeX grows, so does the desire to push its capabilities beyond the basics. This chapter explores a range of advanced features and techniques that allow for greater customization, automation, and control over your document’s appearance and behavior. Whether you are typesetting a large thesis, writing a collaborative paper, or preparing a complex technical report, mastering these topics will significantly enhance your efficiency and output quality. In this chapter, we explore sophisticated layout manipulation, including custom page styles, conditional formatting, and advanced document structuring. You will learn how to define and manage new environments, work with counters and lengths, and create professional-quality front matter and appendices. Special emphasis is placed on designing modular document, splitting large projects into manageable components, and optimizing your codebase for readability and reuse. Additionally, we explore how to automate tasks within LaTeX, from creating custom loops and macros to integrating with external tools like Makefile or lilypond-book. For those interested in building reusable templates or creating class files for journals, institutions, or publishers, this chapter also provides foundational insight into defining your own document classes and packages. By the end of this chapter, you will be equipped with the skills to craft highly tailored, professional documents and to leverage LaTeX as a full-fledged typesetting system capable of handling the most demanding publishing requirements.