The main difference between SEM vs. SEO is that SEM is a paid strategy, it is a powerful advertising channel. It is a technique of diverting more traffic towards the website by increasing the rank of the website on popular search engines like Google, Bing, etc. SEM is also called Search Marketing. It can be done in two ways; by getting traffic to the website with the help of SEO and by getting traffic with the help of SEA. Whereas, Search Engine Optimization (SEO) is the process of getting traffic from the “free,” “organic,” “editorial,” or “natural” listing on search engines. Search Engine Optimization (SEO) increases the visibility of a website or a web page to users of a web search engine. While SEA is a technique of gaining traffic to a website through paid advertising like Google Adwords or PPC (Pay-per-Click advertising).