Link building is important for SEO because search engines like Google consider links to a website as votes of confidence or endorsements from other websites. The more high-quality, relevant links a website has pointing to it, the more likely it is to rank higher in search engine results pages (SERPs) for relevant search queries. In addition, links can also help search engines discover new pages and understand the relationship between different pages and websites. However, it is important to note that not all links are created equal and that quality and relevance are crucial factors in link building success.