Tech moves fast! Stay ahead of the curve with Techopedia! Join nearly 200,000 subscribers who receive actionable tech insights from Techopedia. Cost per impression (CPI) refers to the rate that an advertiser has agreed to pay per 1,000 views of a particular advertisement. A website that serves ads based on CPI doesn’t need the user to click on the ad – each appearance of the ad in front of a user counts as one impression. The advertiser agrees to pay the website a certain price for every 1,000 impressions the ad receives. Cost per impression is also known as cost per thousand, or CPM (the letter "M" is the Roman numeral for 1,000). A CPI arrangement is more common with large websites that represent a branding opportunity for advertisers. CPI follows a pricing model that is closer to the print style of ad sales, with advertisers paying a set price just to show their ads. The website’s ad server monitors the number of impressions and usually adjusts the display rate to match a given advertiser's desired spend on a monthly or quarterly basis.