Generative Engine Optimization (GEO) has become a fast-growing area in digital marketing, helping brands appear inside AI-generated answers from platforms such as ChatGPT, Google AI Overviews, Gemini, Claude, Copilot, and Perplexity. Modern AI systems follow a retrieval process that starts with user intent, searches trusted sources, compares each source for quality, and selects only a small set of passages before generating a natural answer. This retrieve, rerank, and generate pipeline leaves little room for weak content, meaning AI visibility now depends on retrieval quality instead of search ranking alone. Most platforms collect only dozens or a few hundred candidate documents for each query, and a reranking model checks relevance, authority, freshness, and trust. Visibility depends on several connected stages, including retrieval, reranking, context selection, citation, and answer generation. Google AI Overviews now reach more than 2.5 billion monthly users, while ChatGPT serves around one billion weekly users. AI assistants answer a large share of online questions before visitors open traditional search results, creating more zero-click searches and fewer direct website visits. Several studies report that AI referral traffic has grown sharply, even as click-through rates from traditional search decline. Success in GEO is measured through AI mentions, citations, referral traffic, and share of voice, with structured, trustworthy, and well-cited content improving the chances of AI citations.