Whereas Google is easily the most popular website in the world, Baidu is the most popular website in China. It's where China's 1 billion (and growing) internet users go to search.
In principle, paid search ads on Baidu work just like Google AdWords. You bid on keywords, write ad copy, pay per click, and the account management interface looks familiar. Yet that's where the similarities stop. To succeed on Baidu requires at minimum:
You need to know Chinese - not just to choose the right keywords and write compelling ad copy, but the account management interface is all in Chinese too. Same if you need to talk to Baidu support.
It's 100% possible to register a .cn domain name and launch a website with content in Chinese, but if you want to use Baidu SEM to send traffic to your site, you will need to first have an Internet Content Provider (ICP) license issued by the government before Baidu will even let you open an ad account. This process may take a month or longer. The reason for this is Baidu doesn't want to be seen taking money sending internet users to sites not vetted by the government.
Not only because your website will be faster, but again to put Baidu at ease that the government can easily vet and take down your server if it's causing social harm. Baidu doesn't want to be seen stirring up trouble sending Chinese internet users to dangerous foreign websites beyond the reach of government control.
Not only is there more paid search ads on the page, but it's possible for multiple ads to display images (unlike Google which only lets the top-ranked ad display an image, and only if that advertiser is whitelisted). There's also a knowledge panel and a "hot searches" panel to the right of search results. Searchers are much more distracted than they'd be on Google therefore your ad really has to be compelling.
Furthermore if you're used to bidding on your competitors' names to siphon potential customers away from them, that's also more difficult on Baidu because of BrandZone, a feature that allows you to show a huge ad taking up the majority of the screen space for your brand keywords.
Next to each ad on Baidu there is a blue V symbol with either a 1, 2, or 3 next to it. V3 means your website has the highest level of trust with Baidu and a website with a higher V symbol will outrank a website with a lower V symbol, all else equal.
Baidu may be the biggest search engine, but just because Google is no longer competing in China doesn't mean there's not others. The second most popular search engine in China is Shenma, a mobile-only search engine backed by Alibaba.
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