Caller ID spoofing is a spoofing attack which causes the telephone network's Caller ID to indicate to the receiver of a call that the originator of the call is a station other than the true originating station. This can lead to a display showing a phone number different from that of the telephone from which the call was placed.

The term is commonly used to describe situations in which the motivation is considered malicious by the originator.

One effect of the widespread availability of Caller ID spoofing is that, as AARP published in 2019, "you can no longer trust call ID."

Caller ID spoofing has been available for years to people with a specialized digital connection to the telephone company, called an ISDN PRI circuit. Collection agencies, law-enforcement officials, and private investigators have used the practice, with varying degrees of legality. The first mainstream caller ID spoofing service was launched U.S.-wide on September 1, 2004 by California-based Star38.com. Founded by Jason Jepson, it was the first service to allow spoofed calls to be placed from a web interface. It stopped offering service in 2005, as a handful of similar sites were launched.

Caller ID spoofing also has been used in purchase scams on web sites such as Craigslist and eBay. The scamming caller claims to be calling from Canada into the U.S. with a legitimate interest in purchasing advertised items. Often the sellers are asked for personal information such as a copy of a registration title, etc., before the (scammer) purchaser invests the time and effort to come and see the items for sale. In the 2010 election, fake caller IDs of ambulance companies and hospitals were used in Missouri to get potential voters to answer the phone. In 2009, a vindictive Brooklyn wife spoofed the doctor's office of her husband's lover in an attempt to trick the other woman into taking medication which would make her miscarry.

Caller ID spoofing has been used for prank calls, sometimes with devastating consequences. In December 2007, a teenager in Washington used a caller ID spoofing service to send a SWAT team to an unsuspecting victim's house. In February 2008, a man from Collegeville, Pennsylvania was arrested for making threatening phone calls to women and having their home numbers appear "on their caller ID to make it look like the call was coming from inside the house."

In March 2008, several residents in Wilmington, Delaware, reported receiving telemarketing calls during the early morning hours, when the caller had apparently spoofed the caller ID to evoke Tommy Tutone's 1981 hit "867-5309/Jenny". By 2014, an increase in illegal telemarketers displaying the victim's own number, either verbatim or with a few digits randomized, was observed as an attempt to evade caller ID-based blacklists.

In the Canadian federal election of May 2, 2011, both live calls and robocalls are alleged to have been placed with false caller ID, either to replace the caller's identity with that of a fictitious person (Pierre Poutine of Joliette, Quebec) or to disguise calls from an Ohio call centre as Peterborough, Ontario, domestic calls. See Robocall scandal.