This chapter reframes prompt engineering as a systemic practice embedded within real-world tools, platforms, and institutional workflows. It moves beyond individual prompt–response interactions to examine how prompts function as invisible infrastructure that shapes user experience, behavior, and access to knowledge at scale. The discussion introduces systemic prompting as a form of sociotechnical design, where prompts operate through interfaces, no-code systems, and automated workflows. It highlights the ethical implications of hidden prompts, including risks of bias, cultural homogenization, and loss of user agency. The chapter examines common system failures and emphasizes the importance of feedback loops, observability, and version control for maintaining reliability and accountability. It analyzes key deployment patterns, chat-based assistants, background generators, agent pipelines, and simulation systems, demonstrating their benefits and associated risks. Prompt governance is presented as an institutional responsibility requiring traceability, auditability, and shared oversight. The discussion further addresses the urgency of multilingual and cross-cultural prompting, emphasizing linguistic equity as a foundational design principle. Equity-driven solutions are proposed to support inclusive, localized, and culturally responsive AI systems. Ultimately, the chapter positions prompt engineering as a form of infrastructure design that carries long-term ethical, social, and institutional responsibility.