Topic clusters are a content architecture where you organize related content around a central hub-and-spoke model instead of isolated blog posts. A pillar page covers a broad topic at a high level—say, 3,000–5,000 words on "SEO for ecommerce"—while 8–15 cluster pages each tackle a specific subtopic like "product page optimization" or "schema markup for products." Every cluster page links back to the pillar, and the pillar links out to all clusters. This internal linking signals to Google that your site has depth and authority on the topic. The model emerged around 2017 when HubSpot published their framework, responding to how search engines shifted from keyword matching to semantic understanding. Instead of ranking individual pages in isolation, Google now evaluates whether your site comprehensively covers a topic. A tight cluster proves you're not just chasing keywords—you've built real expertise. At Ottawa SEO, we use topic clusters for competitive niches where a single page won't cut it. For a local HVAC client, we built a pillar on "residential heating systems" with clusters on heat pumps, furnace maintenance, and energy rebates. The pillar ranked for the head term within four months, and clusters pulled in long-tail traffic that converted at 4–6%, double the site average. The tradeoffs: clusters require upfront planning and content volume. You need distinct subtopics that warrant their own page—don't artificially split content just to fill the model. Each cluster should target 1,200+ words and a unique search intent. If you're a small business with limited resources, one well-executed cluster beats five half-done ones. Watch out for keyword cannibalization. If your pillar and a cluster target nearly identical keywords, they'll compete. Use clear intent differentiation: the pillar answers "what is X" broadly, while clusters answer "how to do Y" or "when to use Z." Internal anchor text should be descriptive, not generic "click here" links. Done right, topic clusters turn your site into a semantic hub that captures traffic across the buyer journey, from awareness to decision.