The two main types of search engine marketing are SEO (Search Engine Optimization) and PPC (Pay-Per-Click) advertising. SEO involves optimizing a website to increase its ranking in the organic search results without paying for placement. PPC, a component of SEM, involves buying ads that appear in search engine results. Advertisers pay a fee each time one of their ads is clicked. Both strategies aim to increase visibility and traffic to a website but use different methods to achieve these goals.