The iPod is a portable media player designed and marketed by Apple and launched on October 23, 2001. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the iPod Nano, and the compact iPod Shuffle. iPod Classic models store media on an internal hard drive, while all other models use flash memory to enable their smaller size (the discontinued Mini used a Microdrive miniature hard drive). As with many other digital music players, iPods can also serve as external data storage devices. Storage capacity varies by model, ranging from 2 GB for the iPod Shuffle to 160 GB for the iPod Classic. All of the models have been redesigned multiple times since their introduction. The most recent iPod redesigns were introduced on September 1, 2010.

Apple's iTunes software can be used to transfer music to the devices from computers using certain versions of Apple Macintosh and Microsoft Windows operating systems. For users who choose not to use iTunes or whose computers cannot run iTunes, several open source alternatives are available for the iPod. iTunes and its alternatives may also transfer photos, videos, games, contact information, e-mail settings, Web bookmarks, and calendars to iPod models supporting those features.

The iPod branding is also used for the media player applications included with the iPhone and iPad; the iPhone version is essentially a combination of the Music and Videos apps on the iPod Touch. Both devices can therefore function as iPods, but they are generally treated as separate products.

Discontinued models of the line include the iPod Mini and the iPod Photo, which was since reintergrated into the iPod Classic.

The iPod line came from Apple's "digital hub" category, when the company began creating software for the growing market of personal digital devices. Digital cameras, camcorders and organizers had well-established mainstream markets, but the company found existing digital music players "big and clunky or small and useless" with user interfaces that were "unbelievably awful," so Apple decided to develop its own. As ordered by CEO Steve Jobs, Apple's hardware engineering chief Jon Rubinstein assembled a team of engineers to design the iPod line, including hardware engineers Tony Fadell and Michael Dhuey, and design engineer Jonathan Ive. The product was developed in less than one year and unveiled on 23 October 2001. Jobs announced it as a Mac-compatible product with a 5 GB hard drive that put "1,000 songs in your pocket."

Apple did not develop the iPod software entirely in-house, instead using PortalPlayer's reference platform based on two ARM cores. The platform had rudimentary software running on a commercial microkernel embedded operating system. PortalPlayer had previously been working on an IBM-branded MP3 player with Bluetooth headphones. Apple contracted another company, Pixo, to help design and implement the user interface under the direct supervision of Steve Jobs. As development progressed, Apple continued to refine the software's look and feel. Starting with the iPod Mini, the Chicago font was replaced with Espy Sans. Later iPods switched fonts again to Podium Sans—a font similar to Apple's corporate font, Myriad. iPods with color displays then adopted some Mac OS X themes like Aqua progress bars, and brushed metal meant to evoke a combination lock. In 2007, Apple modified the iPod interface again with the introduction of the sixth-generation iPod Classic and third-generation iPod Nano by changing the font to Helvetica and, in most cases, splitting the screen in half by displaying the menus on the left and album artwork, photos, or videos on the right (whichever was appropriate for the selected item).

In September 2007, during a lawsuit with patent holding company Burst.com, Apple drew attention to a patent for a similar device that was developed in 1979. Kane Kramer applied for a UK patent for his design of a "plastic music box" in 1981, which he called the IXI. He was unable to secure funding to renew the US$ 120,000 worldwide patent, so it lapsed and Kramer never profited from his idea.

All iPods except for the iPod Touch can function in "disk mode" as mass storage devices to store data files but this may not be the default behavior, and in the case of the iPod Touch, requires special software. If an iPod is formatted on a Mac OS X computer, it uses the HFS+ file system format, which allows it to serve as a boot disk for a Mac computer. If it is formatted on Windows, the FAT32 format is used. With the release of the Windows-compatible iPod, the default file system used on the iPod line switched from HFS+ to FAT32, although it can be reformatted to either file system (excluding the iPod Shuffle which is strictly FAT32). Generally, if a new iPod (excluding the iPod Shuffle) is initially plugged into a computer running Windows, it will be formatted with FAT32, and if initially plugged into a Mac running Mac OS X it will be formatted with HFS+.

Unlike many other MP3 players, simply copying audio or video files to the drive with a typical file management application will not allow an iPod to properly access them. The user must use software that has been specifically designed to transfer media files to iPods, so that the files are playable and viewable. Usually iTunes is used to transfer media to an iPod, though several alternative third-party applications are available on a number of different platforms.

iTunes 7 and above can transfer purchased media of the iTunes Store from an iPod to a computer, provided that computer containing the DRM protected media is authorized to play it.

Media files are stored on an iPod in a hidden folder, along with a proprietary database file. The hidden content can be accessed on the host operating system by enabling hidden files to be shown. The media files can then be recovered manually by copying the files or folders off the iPod. Many third-party applications also allow easy copying of media files off of an iPod.